Inkjet head

1. An inkjet head comprising:

a flow path unit including pressure chambers arranged along a plane, and which is connected to nozzles respectively; and

an actuator unit fixed to a surface of the flow path unit, which changes volume of each of the pressure chambers, the actuator unit including:

individual electrodes each having a main electrode region disposed in a position opposite to corresponding pressure chambers; and a sub electrode region continued to the main electrode region and connected to a signal line;

a common electrode laid over the pressure chambers; and

a piezoelectric sheet disposed between the common electrode and the individual electrodes, wherein

the flow path unit includes at least one overhang portion provided in the pressure chambers and formed in such a manner that at least amount of protrusion of each side wall of each pressure chamber in a direction along the plane at a top height level as the height nearest to the actuator unit is larger than an amount of protrusion of each of side walls of each pressure chamber in the direction along the plane at any height level different from the top height level on an assumption that the height level is virtually provided in a direction from the pressure chamber to the actuator unit, and

each sub electrode region is disposed between a position where a center of the sub electrode region at least partially overlaps an outer edge of a corresponding overhang portion on a side facing the pressure chamber at the top height level and a position where the sub electrode region does not overlap a corresponding overhang portion at the top height level but an outer edge of the sub electrode region overlaps an outer edge of a corresponding overhang portion on a side not facing the pressure chamber.

2. An inkjet head according to clam 1 , wherein

the center of each sub electrode region overlaps a corresponding overhang portion at the top height level.

3. An inkjet head according to clam 2 , wherein

a whole of each sub electrode region overlaps the corresponding overhang portion at the top height level.

4. An inkjet head according to claim 2 , wherein the main electrode is included in a center region of each of the pressure chambers defined by the outer edge of the overhang portion on the side facing the pressure chamber and an outer edge of each of the pressure chambers.

5. An inkjet head according to claim 1 , wherein

each of the pressure chambers is shaped like at least one of parallelogram and a corner-rounded parallelogram having two acute-angled portions in plan view so that the each sub electrode region at least partially overlaps the overhang portion provided in one of the two acute-angled portions of the corresponding pressure chamber.

6. An inkjet head according to claim 1 , wherein

the individual electrodes and the pressure chambers are disposed in the form of a matrix so that the sub electrode region of each individual electrode is located between the main electrode regions of other two individual electrodes.

7. An inkjet head according to claim 1 , wherein

the each overhang portion has a region in which the amount of protrusion in the direction along the plane decreases as the height level becomes farther than the top height level.

8. An inkjet head according to claim 1 , wherein

the flow path unit includes a plurality of sheet members laminated on one another; and

the overhang portions are formed in such a manner that one of the sheet members used for forming at least part of spaces of the pressure chambers is etched from a surface opposite to the nozzles.

9. An inkjet head according to claim 1 , wherein

the flow path unit includes a plurality of sheet members laminated on one another; and

the overhang portions are formed in such a manner that one of the sheet members used for forming at least part of spaces of the pressure chambers is etched from opposite surface of the one of the sheet members.

10. An inkjet head according to claim 1 , wherein

the flow path unit includes a plurality of sheet members laminated on one another; and

the overhang portions are formed in such a manner that the at least two sheet members having holes are laminated on each other so that the positions of outer edges facing the holes are different from each other.

11. An inkjet head comprising:

a flow path unit including pressure chambers arranged along a plane, and which is connected to nozzles respectively; and

an actuator unit fixed to a surface of the flow path unit, which changes volume of each of the pressure chambers, the actuator unit including:

individual electrodes each having a main electrode region disposed in a position opposite to corresponding one of the pressure chambers; and a sub electrode region continued to the main electrode region and connected to a signal line;

a common electrode kept at common electric potential; and

a piezoelectric sheet put between the common electrode and the individual electrodes so as to be laid over the pressure chambers, wherein

the flow path unit includes at least one overhang portion provided in the pressure chambers and formed in such a manner that at least amount of protrusion of each of side walls of each pressure chamber in a direction along the plane at a top height level as the height nearest to the actuator unit is larger than an amount of protrusion of each of side walls of each pressure chamber in the direction along the plane at any height level different from the top height level on an assumption that the height level is virtually provided in a direction from the pressure chamber to the actuator unit, and

each sub electrode region is disposed between a position where a center of the sub electrode region at least partially overlaps an outer edge of a corresponding overhang portion on a side facing the pressure chamber at the top height level and a position where the sub electrode region does not overlap a corresponding overhang portion at the top height level but an outer edge of the sub electrode region overlaps an outer edge of a corresponding overhang portion on a side not facing the pressure chamber.