1. Field of the Invention
The present invention relates to an ink jet printer head and particularly to such an ink jet printer head which employs a piezoelectric actuator and has a plurality of ink ejection nozzles and which ejects, from an arbitrary one of the ink ejection nozzles, a droplet of ink by driving or operating the piezoelectric actuator.
2. Discussion of Related Art
Japanese Patent Application Publication No. 2002-36544, Japanese Patent Application Publication No. 2002-19102, or their corresponding U.S. Pat. No. 6,631,981 discloses an on-demand-type ink jet printer head. The disclosed printer head employs a cavity unit which is constituted by a plurality of sheet members stacked on each other and has a plurality of ink channels. Those sheet members include a nozzle sheet having a plurality of ink ejection nozzles; a base sheet having a plurality of pressure chambers communicating with the ink ejection nozzles, respectively; and a manifold sheet having a manifold chamber as a common ink chamber that communicates, at its inlet end, with an ink supply source and, at its outlet ends, with the pressure chambers. The disclosed printer head additionally employs a piezoelectric actuator including a plurality of piezoelectric sheets and a plurality of internal electrodes that are alternately stacked on each other. The plurality of internal electrodes include a plurality of common electrodes and a plurality of individual-electrode layers that are alternate with each other in the direction of stacking of the piezoelectric sheets and the internal electrodes. Each of the individual-electrode layers includes a plurality of individual electrodes that are independent of each other. Thus, the piezoelectric actuator includes a plurality of active portions each of which includes respective one individual electrodes of the individual-electrode layers, respective portions of the common electrodes that are aligned with those respective individual electrodes in the stacking direction, and respective portions of the piezoelectric sheets that are aligned with those respective individual electrodes in the same direction. The piezoelectric actuator is bonded to the cavity unit, such that each of the active portions of the piezoelectric actuator is aligned, in its plan view, with a corresponding one of the pressure chambers of the cavity unit.
The piezoelectric actuator has, on an outer surface of an outermost sheet thereof, a plurality of external individual electrodes that are electrically connected to the internal individual electrodes of each one of the individual-electrode layers, respectively, via a plurality of internal conductive leads extending through a corresponding one of the piezoelectric sheets in the stacking direction; and an external common electrode that is electrically connected to each one of the common electrodes via an internal conductive lead extending through a corresponding one of the piezoelectric sheets in the stacking direction. Each one of the external individual electrodes, and the external common electrode are used to apply an electric voltage to a corresponding one of the active portions of the piezoelectric actuator. To this end, the external individual and common electrodes of the piezoelectric actuator are bonded to respective connection electrodes of a flexible flat cable which transmits control signals supplied from an external device.
In the disclosed printer head, however, the external individual and common electrodes are located, on the outer surface of the piezoelectric actuator, along opposite end portions of the outer surface that extend in a lengthwise direction thereof, i.e., in a direction in which the ink ejection nozzles are arranged in one or more arrays. Consequently a great number of lead wires which are connected, at respective one ends thereof, to the connection electrodes and are connected, at respective other ends thereof, to an external driver IC (integrated circuit) are formed in narrow portions of the flexible flat cable that correspond to the above-indicated opposite end portions of the outer surface of the piezoelectric actuator. Therefore, as a total number of the ink ejection nozzles or the active portions increases, a distance between each pair of lead wires located adjacent each other decreases, and accordingly a mutual inductance produced between the each pair of adjacent lead wires increases. This leads to lowering a printing performance of the printer head.
In this background, Japanese Patent Application Publication No. 2001-260349 or its corresponding U.S. Pat. No. 6,604,817 has proposed to prevent the increasing of the above-indicated mutual inductance by connecting the flexible flat cable to the outer surface of the piezoelectric actuator, such that the flat cable extends in a direction perpendicular to the lengthwise direction of the outer surface, and form the thin lead wires such that the lead wires are distant from each other in the direction in which the arrays of ink ejection nozzles extend.