Ink level indicator and ink cartridge having the same

#This invention relates generally to an ink level indicator and an ink cartridge having the same and, more particularly, to ink level indicator for use in a vented foam-filled ink jet print cartridge having a window for residual ink level indication.

#The problem of monitoring the ink volume or ink level in all types of ink-jet printers with ink reservoirs has been variously addressed. So-called backpressure indicators require a plurality of complex seals within the ink cartridge assembly and are therefore relatively expensive and tend to be unreliable. Other ink volume indicators rely on a system that measures the ink bulk electrical conductivity. The electrical conductivity of ink is difficult to control and there is likelihood that future ink improvements could make such a system obsolete.

#There have also been attempts in systems to count the “dots” or ink drops dispensed from an ink jet print cartridge. The counters, actuators and sensors needed for such systems may cause the systems to be relatively expensive to build. Furthermore, accuracy may be compromised by the need to assume an average drop volume for all print cartridges. Interruptions such as caused by removal of a print cartridge from a printer or shut-down of the printer are a possible further source of unreliability since the record of the number of drops dispensed from the ink jet print cartridge since the last update is likely to be lost.

#The invention will be better understood with reference to the drawings, in which:

#FIG. 1 is an isometric drawing of a multi-chamber vented foam-filled ink jet print cartridge having a wall cut away to show an ink level indicator according to a first embodiment of the present invention;

#FIG. 2 is a perspective drawing showing a bottom plan view of the ink jet print cartridge in FIG. 1;

#Hereafter, preferred embodiments of the present invention will be described in the context of an ink jet print cartridge. However, it is to be understood that the invention is usable with any type of ink cartridge having a reservoir that is filled with a porous material member.

#FIG. 1 shows an isometric drawing of a multi-chamber ink jet print cartridge 2 having a wall cut away to reveal one of three ink level indicators 4 according to a first embodiment of the present invention. The print cartridge 2 has three separate chambers or reservoirs 6 (FIG. 4) for containing three hues of ink. Each of the ink level indicators 4 includes a window 8 that interacts with a porous material member, such as a synthetic foam member 10, in the respective reservoir 6 to indicate to a user the amount of ink residual in the reservoir 6. The window 8 is disposed on the print cartridge 2 to allow a user to view through the window 8 when light falls on the window 8 as shown in FIG. 2. FIG. 3 is a side elevation of the print cartridge 2 having a wall cut away to show one of the ink level indicators 4. FIG. 4 is an exploded drawing of the print cartridge.

#According to one embodiment of the present invention, a window 8a has steps 38a-38e (FIG. 5A) of varying thickness. This window 8a when disposed or pressed against a foam member 10a compresses the foam member 10a by varying amounts to result in foam member sections 36a-36e of varying capillarities adjacent the window 8a. Each of the foam member portions 36a-36e is able to retain a different amount of ink therein for a particular amount of residual ink in a reservoir 6. Each of the foam member portions 36a-36e thus appears different from the other foam member portions when viewed through the window to provide an indication of the particular amount of residual ink.