I'm taking apart a Canon Pixma MX340 multi-function inkjet and it took a while to work my way down to the actual printing mechanisms in its base. There were a lot of interesting parts near the print head parking area, including a mystery gearbox I can't access until later. For now I know only it has several gears and a photo interrupter sensor, and it's involved in the paper feed process.

One of the gears is connected via a shaft to the paper feed roller, which has its own corresponding spring-loaded lever + photo interrupter sensor to detect when a sheet of paper has been fed through.

The tired old paper feed roller is covered with cracks.

The paper feed path design for this printer is nearly straight, barely bending the sheet of paper as it is fed from the input tray in the back through to the printing area and the output tray in the front. Here we can see two more sets of rollers, one immediately before and immediately after where the print head deposits ink.

Between these two sets of rollers, underneath that print area, is a sponge-looking substance that has soaked up a visible quantity of ink. The surrounding plastic shows plenty of ink stain discoloration as well. I can't explain all of the reasons why ink ended up here instead of on paper, but I know one explanation are from my border-less photo printing on 4" x 6" glossy photo paper. In order to not leave any borders, the print head shoots out extra ink beyond the paper's edge. That ink had to be go somewhere and we're looking at them now.

Now that I know excess ink may get sprayed around even during normal usage, I started noticing ink absorption pads scattered throughout the print engine. I remember reading consumer backlash against Epson EcoTank machines. Advertised to be ideal for high volume inkjet printing, some users were surprised when their machines stopped printing. They had encountered a preprogrammed expiration for ink pads reaching end of life. At the time I agreed with many others online thinking it was just corporate greed shutting down perfectly working printers, but now that I'm looking at these ink pads on my old printer, maybe it's a good idea to avoid overfilling their diapers.

The second set of paper feed rollers helps keep the paper straight during printing, and can help eject the printed sheet at the end. But it needs to solve an unique problem: how does it handle the printout when the ink is still damp immediately after printing? To see how that was done, I unscrewed the top set of rollers and flipped over the mechanism for a closer look.

The top rollers are actually small stamped sheet metal spiked wheels that minimize contact area with the just-printed surface. Thereby avoid smearing still-wet ink as the paper travels through these rollers. Very nice! Next I will look at the motor and gears driving this paper feed mechanism.

This teardown ran far longer than I originally thought it would. Click here for the starting point.