I started taking apart this Canon Pixma MX340 multi-function inkjet from the back panel, but I didn't get very far before I got stuck. Next I'll try another angle, starting from the top. This device has an automatic document feeder (ADF) up top to help scan/fax multi-page documents.

In case of paper jam, this ADF lid flips open to help us clear them. A few fasteners were visible with the lid open, but removing them were not immediately helpful for disassembly. This piece of plastic must be held in place by other things. Two spring-loaded latches on either side of the lid keeps it in place when closed. These latches were interesting because they had to be loose enough to make the lid easy to open, but tight enough to keep the lid in place while the feeder is running. Note the white gear visible towards the top right of this picture, more on that later.

The lid itself were not held by any fasteners at all. Bending a few pieces of plastic were enough to free it from its hinge. This caught my attention because I saw multiple paper feed rollers on this lid, but there were no cables in this hinge.

Power is transmitted to rollers via that gear on the lid's back edge. Turning this single gear activated multiple functions. I can see the dual-roller mechanism flip out from the lid, which would put some pressure on the top sheet of paper in the document feeder. Once this pressure was applied, continuing to turn the gear would start turning rollers to help feed that top sheet into the feeder.

If I were to design a mechanism to do this before seeing Canon's solution, I would have used a servo to put pressure on the roller and a separate motor to turn the roller, two motors -- and associated complexity and potential failure points -- instead of this clever mechanism. This is why I am not working as a mechanical engineer for Canon.

The topmost white plastic piece in this lid were held by a few clips. Once removed, we can see internals of the spring-loaded latches and the roller mechanism.

Friction plays a big part here. The paper feed roller themselves are covered in soft rubber for traction, and that rubber layer has dried and cracked with age. The roller pressure mechanism also works with friction to some degree, tight enough to rotate this mechanism to put pressure on the top sheet of paper but loose enough to allow the rotation force to gracefully transition to turning the paper feed rollers. I expect this friction mechanism to wear down with age, putting less and less pressure on the top document sheet. It's not great to have a mechanism designed to gradually destroy itself, but the fact is, it lasted to retirement. It's not just good, it's good enough!

I enjoyed looking over this unexpectedly complex mechanism, and I've barely started taking the inkjet apart. I hope there are more fascinating details as I continued this teardown.