I'm taking apart my old retired Canon MX340 multi-function inkjet and learning how it worked as I go. Its print head maintenance assembly is my current focus. Tracing through its range of motion, I finally have some answers for a question I had wondered about: why does it get so messy?

Given that inkjet printing required mechanisms that, well, jet out ink, it would be unrealistic to expect everything to stay clean and pristine. The print head needs a place to get primed and readied into a known operating state before it starts actually printing the page. A waste of expensive ink that I had grudgingly accepted as unavoidable. I had expected a sponge to absorb ink sitting below each print head, so I expected some ink splatter around maybe a 5mm perimeter around the print head outline. Once I opened the lid, I saw ink has been flung quite a bit further, up to ~40mm away.

After tracing through this assembly's range of motion I now understand this mess was created by the wiper blades. Held up against the bottom of ink cartridges, they would have wiped off any ink from the surface of the print head. Once the cartridges moved past them, these elastic wiper blades would snap back to their vertical position. Surface tension would keep some ink on the blade, but the rest would launch for a landing elsewhere on this assembly.

There must be a slight angle between a cartridge and its wiper, as ink splatters are not symmetric: there's visibly more ink flung towards the back of the printer (top of picture) than the front. The left-right asymmetry is more obvious and understandable, given the direction of the wiping motion. When these wiper blades snapped back vertical, that first motion would have moved left to right, with most of the energy on that first motion flinging ink to the right. Less (but not zero) ink would have been shed on the second motion to the left.

Curious about how much energy would have been involved, I took a cotton swab to poke at those wiper blades. (I didn't want to get ink on my fingertips.) They have roughly the same flexibility as fresh automotive windshield wiper blades. I had expected them to have hardened up from age, more than a decade since their manufacture. Maybe they've hardened since new, but they're still soft enough to do the job.

Since I already had soaked the tip of the cotton swab with ink, I poked at the rest of the ink-splattered components. All of the white plastic were rigid, no surprises there. There is a black rubber surround for each print head, and they are still very soft and pliable to form a good seal. Useful to keep ink from drying inside the print head.

The center, however, was a surprise. I had expected a soft spongy material to soak up ink, but the mystery material was actually quite rigid. Its surface texture implied some level of porosity like a sponge, but it had none of a sponge's pliability. Very interesting! Maybe I can get more information about how it works by looking underneath.

This teardown ran far longer than I originally thought it would. Click here to rewind back to where this adventure started.