Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2003-05-29
2004-08-31
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S071000
Reexamination Certificate
active
06783212
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ink jet head and an ink jet recording apparatus.
BACKGROUND OF THE INVENTION
An ink jet head using piezoelectric actuators including piezoelectric elements with electrodes provided on both sides thereof is known in the art, as disclosed in Japanese Laid-Open Patent Publication No. 2001-162794. An ink jet head of this type includes a plurality of nozzles, a plurality of pressure chambers associated with the respective nozzles, and a plurality of piezoelectric actuators associated with the respective pressure chambers. Typically, a single “common electrode” is provided on one side of the plurality of piezoelectric actuators so that the common electrode is shared by the piezoelectric actuators. On the other hand, “separate electrodes” are provided independently on the other side of the plurality of piezoelectric actuators. With the ink jet head as described above, a voltage is applied between a separate electrode and the common electrode so as to expand/contract a piezoelectric element, and a pressure is applied on the ink in a pressure chamber by the expansion/contraction, thereby discharging the ink through a nozzle.
An ink jet head is provided with a driving circuit for supplying a driving signal. The driving circuit of a conventional ink jet head has the same number of channels as the number of actuators in order to supply a driving signal individually to the separate electrode of each actuator. The driving circuit is designed so that a pulse signal is applied to an actuator that is to discharge ink while a pulse signal is not applied to an actuator that is not to discharge ink, thus turning the signal ON/OFF individually for each actuator.
With such an ink jet head, however, as the number of actuators increases, the number of channels of the driving circuit increases accordingly, whereby the cost for the driving circuit increases inevitably. With the recent increase in the number of nozzles provided in an ink jet head, the increase in the cost for the driving circuit is becoming non-negligible.
In view of this, an ink jet head employing a so-called “matrix driving” method has been suggested in the art, in which scanning electrodes and counter electrodes are arranged in a matrix pattern, as disclosed in Domestic Republication of PCT Publication WO99/12739. With an ink jet head employing a matrix driving method, the number of channels of the driving circuit can be reduced significantly, and thus the cost for the driving circuit can be reduced.
In an ink jet head employing a matrix driving method as described above, relay terminals connecting the driving circuit with the scanning electrodes, and relay terminals connecting the driving circuit with the counter electrodes, are localized at corners of the head assembly.
As a result, scanning electrode lead wires connecting the relay terminals with the scanning electrodes, and counter electrode lead wires connecting the relay terminals with the counter electrodes, are relatively long. Therefore, the lead wires have relatively high electric resistances.
Moreover, the scanning electrode lead wires and the counter electrode lead wires have different lengths for different scanning electrodes or different counter electrodes. Therefore, signals supplied to different electrodes vary slightly from one another, whereby different nozzles are likely to have varied levels of ink discharging performance. As a result, the recording precision is not sufficiently high. Moreover, while it is necessary, with a matrix driving method, that signals to be applied to the scanning electrodes (hereinafter referred to as “scanning signals”) and signals to be applied to the counter electrode (hereinafter referred to as “recording signals”) need to be precisely synchronized with each other, it is difficult to achieve precise synchronization if signals supplied to different electrodes vary from one another.
Some ink jet heads use a plurality of types of ink. For example, an ink jet head for forming a color image uses a plurality of colors of ink. In such an ink jet head, a plurality of actuators are provided to form a column of actuators for each color. With a conventional ink jet head of this type, the driving circuit supplies the same driving signal to actuators of the actuator columns for all colors.
However, properties of ink such as the viscosity vary among different types of ink. Therefore, even if the same driving signal is applied, the difference in the type of ink results in a difference in the ink discharging performance.
In view of this, in the prior art, types of ink are chosen, or the physical properties of different types of ink are adjusted, so that the ink discharging characteristics are made uniform among the different types of ink. However, this imposes a certain limitation on the types of ink that can be used.
Another way is to adjust a driving signal for each type of ink. However, with such an ink jet head, as disclosed in Japanese Laid-Open Patent Publication No. 2001-162794, the configuration of the driving circuit may become complicated, leading to other problems such as an increase in the cost for the driving circuit and a decrease in the reliability in controlling the ink discharge.
Note that these problems occur not only when a plurality of types of ink are used, but also when there are variations in the actuator characteristics or the pressure chamber size among different actuator columns.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above. An object of the present invention is to shorten a lead wire connecting a relay terminal with an electrode. Another object of the present invention is to suppress the variations among signals supplied to different electrodes, thereby improving the ink discharging performance. Still another object of the present invention is to precisely synchronize the scanning signal with the recording signal. Yet another object of the present invention is to provide a technique that allows easy adjustment of a driving signal for each column without complicating the configuration of the driving circuit.
An ink jet head of the present invention includes: a head assembly provided with a plurality of nozzles and a plurality of pressure chambers storing ink therein and communicated respectively to the nozzles; actuators each associated with one of the pressure chambers and each including a piezoelectric element, a scanning electrode provided on one side of the piezoelectric element, and a recording electrode provided on the other side of the piezoelectric element, wherein the actuators are arranged in a matrix pattern of n rows by m columns (where n and m are natural numbers equal to or greater than two) in terms of electrical circuit, with the recording electrodes of each row being electrically connected to one another, and the scanning electrodes of each column being electrically connected to one another; and a driving circuit for supplying a scanning signal to the scanning electrodes for each column, while supplying a recording signal to each row of the recording electrodes in synchronization with the scanning signal, wherein: the actuators are geometrically arranged in n rows by m columns on the head assembly; a relay terminal, extending in a vertical direction, is provided in at least one inter-column space between vertical columns of the actuators on the head assembly for relaying signals from the driving circuit to the recording electrodes and the scanning electrodes; and the recording electrodes and the scanning electrodes are connected to the relay terminal via lead wires extending in a horizontal direction.
In this ink jet head, the relay terminal extends in the vertical direction, and the lead wires connecting the relay terminal with the recording electrodes and the scanning electrodes extend in the horizontal direction, whereby it is not necessary to extend the lead wires in a complicated pattern, e.g., a meandering pattern, and it is thus possible to reduce the length of the lead wires. Moreover, since the relay ter
Baba Koichi
Ikeda Kouji
Oyama Masaharu
Dudding Alfred
Harness & Dickey & Pierce P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Meier Stephen D.
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