Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2003-03-25
2004-11-23
Nguyen, Judy (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06820969
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid-jet head that ejects jets of liquid and to a liquid-jet apparatus. More particularly, the present invention relates to an ink-jet recording head that pressurizes, by piezoelectric elements, ink supplied to pressure generating chambers communicating with nozzle orifices that eject ink droplets to eject the ink droplets from the nozzle orifices, and relates to an ink-jet recording apparatus.
2. Description of the Related Art
Two types of heads are put into practical use in an ink-jet recording head, in which pressure generating chambers that communicate with nozzle orifices ejecting ink droplets are partially constituted of vibration plate. The vibration plate is deformed by piezoelectric elements to pressurize ink in the pressure generating chambers, and the ink droplets are ejected from the nozzle orifices. One is a recording head using piezoelectric actuators of a longitudinal vibration mode which expand and contract in an axis direction of the piezoelectric elements, and the other is a recording head using piezoelectric actuators of a flexural vibration mode.
In the former type, a volume of each pressure generating chamber can be changed by abutting an end surface of the piezoelectric element against the vibration plate, and manufacturing of a head suitable to high density printing is made possible. On the contrary, while this is possible, it requires a difficult process of cutting and dividing the piezoelectric element in a comb tooth shape in accordance with an array pitch of the nozzle orifices and work of positioning and fixing the cut and divided piezoelectric elements to the pressure generating chambers. Thus, there is a problem of a complex manufacturing process. On the other hand, in the latter one, the piezoelectric elements can be fabricated and installed on the vibration plate by a relatively simple process of adhering a green sheet of a piezoelectric material while fitting a shape thereof to that of the pressure generating chambers and baking the green sheet. However, a certain area of the vibration plate is required due to use of the flexural vibration, thus there is a problem that a high density array of the piezoelectric elements is difficult.
Meanwhile, in order to solve such a disadvantage of the latter recording head, a recording head is proposed, in which an even piezoelectric material layer is formed over the entire surface of a vibration plate by a deposition technology, the piezoelectric material layer is cut and divided into a shape corresponding to that of pressure generating chambers by a lithography method, and piezoelectric elements are formed so as to be independent of each other for each pressure generating chamber (refer to, for example, Japanese Patent Laid-Open No. Hei 5(1993)-286131).
Accordingly, the work of adhering the piezoelectric elements to the vibration plate is eliminated, and there are advantages in that not only can the piezoelectric elements be fabricated and installed by a precise and simple method that is the lithography method but also the thickness of each piezoelectric element can be thinned to enable a high-speed drive.
SUMMARY OF THE INVENTION
However, in the ink-jet recording head in which the piezoelectric elements are arrayed in high density as described above, one electrode (common electrode) is provided commonly to the plurality of piezoelectric elements. Therefore, when a large number of piezoelectric elements are driven simultaneously to eject a large number of ink droplets at one time, a voltage drop occurs and the amounts of displacement of the piezoelectric elements become unstable, causing a problem of lowering ink ejection characteristics. Moreover, a voltage, which is applied to a piezoelectric element provided on a position farther from a terminal portion to which external wiring is connected, is apt to be lowered. Therefore, there is a problem of variations in ejection characteristics of liquid droplets depending on distances from the terminal portion even in piezoelectric elements provided parallel in one row.
Although such problems as described above can be solved by thickening the thickness of the common electrode of the piezoelectric elements, a problem occurs that the amounts of displacement of the vibration plate, which is generated by the drive of the piezoelectric elements, are lowered because the common electrode generally constitutes a part of the vibration plate. Although the problems as described above can be solved also by expanding the area of the common electrode, there is a problem that the head is enlarged. Moreover, an electrode of a piezoelectric element formed of a thin film has a relatively high resistance value because a film thickness thereof is thin, and therefore, the problems as described above are particularly apt to occur therein.
As another means for solving the problems as described above, there is a recording head, in which a plurality of lower electrode films (lower electrodes) are divided into several groups and each common terminal is provided so as to correspond to each of the groups, thus controlling the voltage drop in attempt to equalize the properties of actuators (piezoelectric elements) (refer to, for example, Japanese Patent Laid-Open No. 2002-11877).
With such a structure, the occurrences of voltage drop are able to be controlled; however, the number of terminals is increased to such a great extent that the wiring structure becomes complicated. Therefore, there are problems that the manufacturing process becomes complicated and that it is difficult to adopt the structure when the piezoelectric element is arrayed in high density. Note that such problems needless to say exist in the manufacturing method of other liquid-jet heads that eject something other than ink, similarly to the manufacturing method of an ink-jet recording head that ejects ink.
In consideration of such circumstances as described above, it is an object of the present invention to provide a liquid-jet head that is capable of maintaining the ejection characteristics of the liquid droplets, obtaining stable ejection characteristics and arraying the piezoelectric elements in high density, and to provide a liquid-jet apparatus.
A first aspect of the present invention that attains the foregoing object is a liquid-jet head comprising: a passage-forming substrate in which pressure generating chambers communicating with nozzle orifices are formed; and piezoelectric elements for generating pressure changes in the pressure generating chambers, the piezoelectric elements being provided on one surface side of the passage-forming substrate with vibration plate interposed therebetween, characterized in that a resistance reduction portion is provided to reduce a resistance of a common electrode common to the plurality of piezoelectric elements when a voltage is applied to the piezoelectric elements, the resistance reduction portion including; common lead electrodes extracted from portions of the common electrode, the portions excluding both end portions in a direction where the piezoelectric elements are provided parallel, to outside regions opposite with the pressure generating chambers; and connection wiring composed of a bonding wire.
In the first aspect, the resistance value of the common electrode when a voltage is applied to the piezoelectric elements is substantially lowered by the resistance reduction portion. Therefore, the voltage drop can be prevented from being generated when the plurality of piezoelectric elements are driven simultaneously. Accordingly, the ejection characteristics of liquid droplets are stabilized without being varied. Moreover, the common lead electrodes are connected to one another by a connection wiring composed of a bonding wire, and thus the head is not enlarged, and the piezoelectric elements can be arrayed in high density relatively easily.
A second aspect of the present invention is the liquid-jet head according to the first aspect, characterized in that the plurality of common lead
Nguyen Judy
Seiko Epson Corporation
Sughrue & Mion, PLLC
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