I took apart an old printer yesterday. Some time ago I bought a multifunctional and so I didn’t need the printer anymore(also the black cartridge was dead and I wasn’t going to invest money into a cartridge that costs as much as the printer).
I was interested in salvaging some of the printer parts. It has some interesting mechanisms driven by 2 DC motors, which was a surprise. I was expecting to find stepper motors, but instead of precisely controlling a motor it seems that the printer relies on an optical detection system that uses transparent bands with black stripes. Perhaps in the future I’ll be able to use the cogs and motors for some kind of a robot-machine controlled with Arduino. I think I can also save some capacitors from the circuit board.
The printer also had an interesting ink “pump”. I think I got the idea behind it, after playing a little with the ink cartridge slide mechanism. You know on some printers there are lots of noises before starting a print, among which a weird “locking” noise? Well, at one of the sliding line ends there’s a plastic plate with a hook. When the ink cartridges pass over the hook, the plate locks tightly with the 2 ink cartridges. On this plate there are 2 sponges from which 2 hoses go to the “pump”. The pump is driven by the paper feeder( a long metal bar that pulls the paper into the printer). A small quantity of ink goes to waste( don’t worry, there’s a big paper-like sponge to absorb this, so your printer won’t ever “spill” ink out of it) as this mechanism cleans the nozzles.
Alright! So now back to the subject. I was just curious to see how the ink is stored inside the ink cartridges so I opened both the black and the color one. Pictures:
The empty black ink cartridge alongside with the ink holding sponge.
The black ink sponge. As you can notice, it was never fully filled. Now you can be even more furious when wasting your money on a genuine ink cartridge. Now I might be wrong about this, probably there’s a GOOD reason it’s not filled entirely.
Here’s another shot with the black ink sponge:
The color cartridge! I think now you get the point why the color cartridge is consumed so fast:
The color ink holding sponges taken out:
Another macro shot. The yellow ink sponge got dirty because of me handling it 
Well, at least I learned how the ink is stored in ink cartridges. I always thought it was a reservoir of ink, not ink suspended in sponges. There’s probably a logic reason behind this, but I also think some of the ink will never be used this way. Also, the way the thermal ink cartridges work makes it more probable for the nozzles to get permanently damaged if the sponge dries out( although I guess there’s a protection mechanism for this). Here’s a fragment from Wikipedia, the bold lines are important here:
Most consumer inkjet printers, such as those made by Canon, HP, and Lexmark (but not Epson) use a thermal inkjet; inside each partition of the ink reservoir is a heating element with a tiny metal plate or resistor. In response to a signal given by the printer, a tiny current flows through the metal or resistor making it warm, and the ink immediately surrounding the heated plate is vaporized into a tiny air bubble inside the nozzle. As a consequence, the total volume of the ink exceeds that of the nozzle. An ink droplet is forced out of the cartridge nozzle onto the paper. This process takes a matter of milliseconds.
The printing depends on the smooth flow of ink, which can be hindered if the ink begins to dry at the print head, as can happen when an ink level becomes low. Dried ink can be cleaned from a cartridge print head by gentle rubbing with isopropyl alcohol on a swab or folded paper towel.
The ink also acts as a coolant to protect the metal-plate heating elements − when the ink supply is depleted, and printing is attempted, the heating elements in thermal cartridges often burn out, permanently damaging the print head. When the ink first begins to run low, the cartridge should be refilled or replaced, to avoid overheating damage to the print head.
Now I know that when I refill a cartridge, I should push the syringe as deep as possible, and after having it refilled I should let the cartridge rest a bit so the ink can be equally absorbed by the entire sponge.
What intrigues me is how the ink level detection works, because I couldn’t figure that out. I also can’t figure out why after refilling the sponge the printer still reports the ink level as low.
