One source I found says that Canon uses light from an LED--bounced from a prism at the bottom of the cartridge after ink is depleted--to trigger the "Empty" signal. Epson apparently counts the spurts of ink and calculates the arrival of "empty".
On Fri, 6 Mar 2015 23:03:13 -0800, DaveC wrote as underneath :
Any inkjet that uses chipped cartridges guestimates the emptiness. Old Canon printers certainly used the reflective prism, IP4000 was about the last that had unchipped carts. and thus had an accurate end level warning. I think most printers now would guestimate on the safe side judging by the complaints of half full carts being classed as empty. I dont know if Canon still uses the prisms on their modern chipped carts but I would think probably not as the guestimate method gets you to buy more ink earlier! Someone with one of the more modern Canons will know Im sure! ... HP have had chips since very early days so levels will be guestimated by software. C+
Most older cartridges have open cell foam inside to prevent sloshing in transit. Kinda difficult to design a liquid level sensor that works in foam. Neither dye or pigment type inks are very conductive, so that's not going to work.
Some carts don't have any foam and are often clear or at least translucent. However, they are usually used with dye type inks, which are optically transparent. So, that's not going to work.
Older HP color carts have 3 colors in one cartridge. 3 sets of optical sensors in one cart isn't exactly economical or practical.
Optical sensing might work with pigment type inks, but I suspect the optical transmission characteristics will vary with the color. Also yellow is nearly transparent.
There is one place where optical sensing works... laser printers. The toner is optically opaque. Brother printers have windows on each end of the cartridge. Then the light can be seen through the cartridge, it's considered out of toner. The problem is they located the windows a bit too high on some printers. I forgot the model, but one of their older color laser printers leaves about 25% in the cartridge when it claims it's empty. The fix is to put some electrical tape over one of the windows.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Or a vertical light path from the led chip on the bottom of the cartridge, up through the (now) empty cartridge, reflecting off of a prism inside the top of the cartridge back to a receiver on the same chip as the LED is mounted.
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