System and method for maintaining ink concentration in a system

Claim 1

In an ink jet printer having a main ink reservoir as the internal source of ink which is fluidically connected to two external supplies, one of ink and one of ink replenisher, and in which print drops are continuously created and certain of the drops are selected for printing while the drops not selected for printing are returned to the main ink reservoir, the system comprising: (a) a print head connected to receive ink from the main ink reservoir and having means to form drops of a pre-determined small range of drop volumes; (b) selection means for selecting which of the continuously formed drops are needed for printing to form the desired image; (c) drop count means responsive to said selection means for producing a count signal indicative of a number of drops printed; (d) sensing means in the main ink reservoir utilizing hysteresis in a float switch means, the normal level being a point at which the switch assumes a first state, and the low level being a point at which the switch assumes a second state, the sensing means being used to generate a signal responsive to a predetermined low ink level in the reservoir, the difference between an accepted ink level and the low ink level corresponding to a predetermined cycle volume; and (e) control means responsive to the sensing means and the drop count means, the control means including, (a) means for initializing an ink volume variable, a replenishment fluid volume variable, and the count signal, (b) means associated with the sensing means for determining the float switch state, and (c) means associated with the drop count means for constantly updating the count signal as drops are printed, to enable flow of fluid from one of the external reservoirs to the main ink reservoir in response to the low ink level signal means and to cease allowing flow in response to the acceptable ink level signal means.