Abstract: Substantially optimum print quality is maintained for an ink jet printer which includes a nozzle plate having a number of orifice openings from which ink droplets for printing are sprayed. It is electronically determined when a particular orifice opening has been inactive for a predetermined period of time, and then an exercise print command is supplied to the orifice causing an ink droplet to dribble out of the orifice, rather than being sprayed out of the orifice, to keep the orifice clear for printing when a print command is supplied to it. The dribbling drops have a smaller size than the sprayed drops, and may be formed by supplying heater elements associated with the openings with pulses of shorter duration than normal. Dribbling ink droplets are automatically removed from the printer cartridge by one or more strands (e.g. continuous filament rayon thread) moving past the nozzle at a speed of between about 1-3 feet per hour while being positively guided.

Abstract: A method and assembly varies the image density of ink from a plurality of ink jet nozzles to provide substantially uniform ink density. Electronically and automatically the electrical power consumption of an ink jet device having an electrical heater is measured (typically by measuring the current draw), and in response to that measurement, if necessary, pulse or voltage supplied to the heater or heaters of each of the ink jet devices is automatically adjusted. More electrical power is supplied if greater image density is required for a particular ink jet device, and less electrical power if lower image density is desired. During typical operation all pulse widths are reset to default settings, the signal received is calibrated, a pattern generator is signalled to provided test data, the present peak electrical current consumed by each nozzle heater is sampled, and the pulse width for each nozzle heater is set based upon the current sample.

Abstract: In a printer assembly having a rack of ink-jet print cartridges, a backup cartridge is moved into alignment with a cartridge to be cleaned and the backup cartridge substitutes for printing of the cartridge being cleaned until the cleaned cartridge is moved back to its printing position. The backup cartridge is then moved into alignment with another cartridge and prints for that cartridge which is then cleaned. Ink-jet print cartridges must be periodically cleaned to wipe excess ink and particles from the nozzle array on the front face of the cartridge. Cartridges are cleaned by moving them to a cleaning station that wipes clean the front face of the cartridge. To avoid interruption of printing while cartridges are being cleaned, a backup cartridge is moved into alignment and substitute prints for a cartridge to be cleaned.