Development of the HP DeskJet 1200C print cartridge platform - includes related articles on ink cartridges for large-format color plotters and of design of print cartridges for environmental responsibility - design of ink cartridges for HP DeskJet 1200C and HP DeskJet 1200C/PS printers and HP DesignJet 650C plotter - Technical

Hewlett-Packard Journal, Feb, 1994

Plastic tape is used to seal the nozzles during shipping and storage, thus preventing failure of the device as a result of orifices becoming clogged by contamination or dried and crusted ink. The tape must seal securely on the nozzle plate but must also be easily removed before use without damaging the print cartridge or leaving any adhesive residue on the nozzle plate. Tape manufacturing and alignment considerations result in the tape being considerably wider than the nozzle plate so that it extends over the encapsulant beads (see Figs. 5a and 5b). This resulted in a peeling load on the tape in the nozzle region. During high-temperature storage the tape peeled off over the nozzles, leading to wicked ink and some crusted ink nozzle plugs (Fig. 5c). The solution is two slits in the tape just before assembly to decouple the regions of tape over the nozzles and over the encapsulant beads (Fig. 5d). The free end of the tape is then wrapped over a printed paper customer pull tab to provide an easy method of removal.

Ink Level Indicator

During the initial design phase of the Deskjet 1200C print cartridge it was decided that the cartridge should have an ink level indicator. The primary intent of this indicator is to warn the customer so as to prevent losing a printed page because of a print cartridge that is out of ink. The Deskjet 1200C print cartridge will be the first HP inkjet print cartridge with an ink level indicator. Consumer demand for level information is increasing, fueled by indicators in copiers and laser printers showing toner cartridge life and by the larger volumes of printing customers are doing. Knowing a print cartridge is low on ink is helpful before printing a large number of graphics pages. It gives the user time to purchase a replacement print cartridge, provides an indication of which of the color print cartridges is empty, and identifies whether a print cartridge that does not print properly is out of ink or has another problem such as a deprime.

More than 20 methods of implementing an ink level indicator were considered but most either did not meet the required objectives or were too expensive. Building the print cartridge with clear covers and clear films would be very difficult to achieve, and even if achievable would not give the customer a clear ink level indication since the ink level does not drop in a spring-bag print cartridge. Measuring the bulk conductivity of the ink and counting the drops a print cartridge has fired were two of the leading alternatives. The current design has many advantages over these, a primary advantage being that the ink level indicator is independent of the printer.

The design selected is called the dual-flag design (Fig. 6). It consists of two strips (flags) of film attached to either side of the spring bag. One flag is solid green and the other is black and has a rectangular hole cut in it. The flags overlap across the front of the print cartridge with the black flag over the green so that the green can be viewed through the hole in the black flag. An adhesive label covers both flags and provides a window to the indicator. As the ink volume decreases, the two sides of the bag collapse towards each other, moving the flags with them. The amount of overlap indicates the approximate amount of ink remaining in the print cartridge (Fig. 7). The amount of ink is indicated regardless of whether the two sides of the spring bag collapse together or not. When the print cartridge reaches low ink, no green is visible in the viewing window, only black. One half of the black rectangle in the viewing window is the black flag. The other half is actually the print cartridge body showing through the hole in the black flag.