Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-04-23
2004-09-28
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06796631
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of determining the value of a driving voltage applied to a piezoelectric ink jet print head and adjusting the ink ejection condition of the print head.
2. Description of Related Art
An ink jet print head is provided in an ink jet printer. There has been proposed that a piezoelectric type ink-jet print head unit is employed as the ink jet print head. In this type of print head unit, a piezoelectric element is provided to each pressure chamber. By applying an electric voltage to the piezoelectric element, the volume of the corresponding pressure chamber decreases, thereby causing ink to be ejected through a nozzle from the pressure chamber.
In order to manufacture this type of print head unit, a plurality of piezoelectric ceramic sheets are prepared. Internal electrode layers are screen-printed on the piezoelectric ceramic sheets. The piezoelectric ceramic sheets are stacked one on another, pressed against one another, and then baked into a single actuator. In the thus produced actuator, a plurality of piezoelectric elements are defined by a plurality of internal electrode sections, which are defined by the internal electrode layers.
A cavity plate is formed with a plurality of pressure chambers. The actuator is then bonded to the cavity plate so that the piezoelectric elements are located in one to one correspondence with the pressure chambers.
A nozzle plate is made from polyimide or the like, and is formed with a plurality of nozzles. The nozzle plate is bonded to the cavity plate, thereby finally obtaining the ink jet print head unit.
SUMMARY OF THE INVENTION
There are, however, variations in the diameters of nozzles formed in the nozzle plate. There are variations also in the characteristics of the piezoelectric elements. Due to these variations, there are variations in the ink ejection performances in the individual ink jet print head units.
Considering this, the driving voltages to be applied to the head units should be determined individually so that each head unit can eject ink with an optimum ejection speed.
In order to determine the driving voltage, it is conceivable to introduce ink in each head unit. How the head unit ejects ink is monitored while changing the driving voltage applied to the head unit. Printed samples are produced based on the ejected ink, and an observer or worker observes the printed samples. Based on the monitored results and on the observation results of the printed samples, the optimum driving voltage is determined for each head unit.
The above-described conceivable driving-voltage determining method, however, suffers from the problem that the inside of the head unit is stained or smeared with ink when ink is introduced into the print head.
Additionally, the above-described driving-voltage determining method depends on the observer's ability, and therefore is unreliable.
When a single print head is configured from several head units for several colors of ink, there arises the case where the driving voltages for the respective head units are determined as different from one another. In such a case, the power source provided in the printer has to be configured to supply several different voltages simultaneously. The costs of manufacturing the power source increases.
In view of the above-described drawbacks, it is an objective of the present invention to provide an improved method of determining the value of the driving voltage for an ink jet print head unit to adjust the ink ejection condition of the head unit, which does not necessitate introducing ink into the print head, which can determine an optimum driving voltage for a head unit with a simple configuration, and which can set the same, single driving voltage to all the head units provided in a single print head.
In order to attain the above and other objects, the present invention provides a method of determining the value of a driving voltage to be applied to an ink jet print head unit, the ink jet print head unit including a cavity plate and a plurality of piezoelectric elements, the cavity plate being formed with a plurality of pressure chambers and a plurality of nozzles, each pressure chamber being filled with ink and being in fluid communication with a corresponding nozzle, the plurality of piezoelectric elements being provided in one to one correspondence with the plurality of pressure chambers, each piezoelectric element being driven by a driving voltage so as to change the pressure inside the corresponding pressure chamber, thereby allowing ink to be ejected through the corresponding nozzle from the corresponding pressure chamber, the method comprising the steps of: determining at least one of a nozzle-diameter average and a capacitance average, the nozzle-diameter average indicating average of diameters of the plurality of nozzles, the capacitance average indicating average of capacitances of the plurality of piezoelectric elements; and determining a driving voltage to be applied to the piezoelectric elements of the ink jet print head unit by using the determined at least one of the nozzle-diameter average and the capacitance average, and based on a predetermined formula, which is indicative of a relationship of the driving voltage with respect to the at least one of the nozzle-diameter average and the capacitance average.
According to the present invention, therefore, it is possible to easily determine a driving voltage, which should be applied to the ink jet head unit, without actually introducing ink to the ink jet head unit to cause the ink jet head unit to eject ink.
The average-determining step may preferably include at least one of the steps of: determining the nozzle-diameter average, by measuring the diameters of all the nozzles in the ink jet print head unit, and by calculating the nozzle-diameter average based on the measured diameters; and determining the capacitance average, by measuring capacitances of all the piezoelectric elements in the ink jet print head unit, and by calculating the capacitance average based on the measured capacitances. In this case, the driving-voltage determining step calculates the predetermined formula by using the determined at least one of the nozzle-diameter average and the capacitance average, thereby determining the driving voltage.
For example, the nozzle-diameter average can be determined as an arithmetic mean, that is, a quotient obtained by dividing the sum total of the diameters measured for all the nozzles by the number of the nozzles. Similarly, the capacitance average can be determined as an arithmetic mean, that is, a quotient obtained by dividing the sum total of the capacitances measured for all the piezoelectric elements by the number of the piezoelectric elements.
The method may further comprise the step of preparing a plurality of ink jet head units. In this case, the average determining step determines at least one of the nozzle-diameter average and the capacitance average for each ink jet head unit, and the driving-voltage determining step determines the driving voltage to be applied to the piezoelectric elements in each ink jet head unit based on the at least one of the nozzle-diameter average and the capacitance average that is determined for the each ink jet head unit. The method may further comprise the steps of: selecting, among the plurality of ink jet head units, several ink jet head units, for which the driving-voltage determining step has determined the driving voltage of substantially the same values; and assembling together the selected several ink jet head units into a single ink jet print head.
In this way, after preparing a plurality of ink jet head units, an optimum driving voltage is determined for each ink jet head unit in the manner described above. Then, several ink jet head units, for which substantially the same driving voltages have been determined, are selected and assembled together into a single print head. Accordingly, it is possible to apply substantially the same driving voltages to all the hea
Brother Kogyo Kabushiki Kaisha
Dudding Alfred E.
Meier Stephen D.
Oliff & Berridg,e PLC
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