Abstract: An image forming apparatus forms test patches with no lowering of image density and no unevenness of image density. The image forming device includes a unit for generating image data for at least one test patch, an image bearing medium on which a latent image of the test patch is formed being based upon the image data generated by the test patch generating unit, developing unit for supplying toner by means of a developing roller onto the latent image so as to manifest the latent image in order to obtain a toner image, a density sensor for detecting a toner density of a toner image in the manifested test patch, and a compensator for compensating the density, being based upon a value of an output from the density sensor. With this arrangement, the test patch generating unit is adapted to create the test patches after the toner on the developing roller is consumed by a quantity corresponding to one turn of the developing roller.

Abstract: By increasing/deceasing electric energy per unit time supplied to heat energy generation means arranged in a liquid chamber having a nozzle, the amount of the ink emitted from the nozzle can be changed to correct a difference in dot diameter which occurs nozzle by nozzle and a change in dot diameter with time and to permit gradational printing.

Abstract: An ink discharging device includes arrayed nozzle holes and corresponding ink flow paths leading thereto. An electrode is provided between the adjacent ink flow paths in such a manner as to be exposed to both of the adjacent ink flow paths so that each electrode works as a common electrode for both of the adjacent ink flow paths. By energizing a conductive ink between the electrodes within the corresponding ink flow path, a portion of the conductive ink is discharged through the corresponding nozzle hole.

Abstract: In an ink-jet printer of the type wherein a current is passed through a conductive ink contained between a pair of electrodes to cause the ink to become vaporized and cause trapped gasses or bubbles to expand suddenly, exerting a sufficient pressure upon the ink to force droplets of ink from a nozzle, a current value flowing between the electrodes is detected to determine the amount of wear of the electrodes, and when the detected current value is lower than a predetermined value, an alarm indicative of the replacement of the currently used ink-jet head is given and, at the same time, ejection of the ink from the nozzle is stopped. Thus, printing operation is always achieved with stable ejection of ink, guaranteeing high printing qualities.