INKJET HEAD

Abstract

An actuator can selectively take a first state wherein a volume of a pressure chamber is V1 and a second state wherein the volume of the pressure chamber is V2 larger than V1. The actuator changes from the first state to the second state and then returns to the first state to eject ink from an ejection port. A proper oscillation period Ts of an oscillation generated by integral deformation of the actuator and the pressure chamber when ink is ejected from the ejection port, and a proper oscillation period Td of ink filling up a first partial passage leading from an outlet of the pressure chamber to the ejection port in an individual ink passage, satisfy a condition that Ts/Td is not less than 0.36 and not more than 0.90; or not less then 1.1 and not more than 1.7.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other and further objects, features and advantages of the invention will appear more fully from the following description taken in connection with the accompanying drawings in which:

FIG. 1 shows a general construction of a printer as an inkjet recording apparatus according to an embodiment of the present invention;

FIG. 2 is an upper view of a head main body shown in FIG. 1;

FIG. 3 is an enlarged view of a region enclosed with an alternate long and short dash line in FIG. 2;

FIG. 4 is a vertically sectional view taken along line IV-IV in FIG. 3;

FIG. 5 is a partial enlarged view near a piezoelectric actuator shown in FIG. 4;

FIG. 6 is a block diagram showing a construction of a controller included in the printer shown in FIG. 1;

FIG. 7 is a graph showing an example of a change in the potential of an individual electrode to which a voltage pulse signal is supplied;

FIGS. BA, 8B, and 8C show a driving manner of a piezoelectric actuator when the potential of an individual electrode changes as shown in FIG. 7 by supplying a voltage pulse signal;

FIGS. 9A, 9B, and 9C show ink droplets ejected from a nozzle when a voltage pulse corresponding to FIG. 7 is supplied to an individual electrode;

FIG. 10A shows an equivalent circuit obtained by modeling an individual ink passage shown in FIG. 4, used in analysis by the inventors of the present invention;

FIG. 10B shows a structure of a first partial passage in a fluid analysis unit shown in FIG. 10A;

FIG. 10C shows a structure of a nozzle in the first partial passage shown in FIG. 10B;

FIG. 11 is a graph showing results of numeric analysis performed by using the model shown in FIGS. 10A to 10C; and

FIG. 12 is another graph showing results of numeric analysis performed by using the model shown in FIGS. 10A to 10C.

Claims

1. An inkjet head comprising: a passage unit comprising a common ink chamber, and an individual ink passage leading from an outlet of the common ink chamber through a pressure chamber to an ink ejection port; andan actuator that can selectively take a first state wherein a volume of the pressure chamber is V1 and a second state wherein the volume of the pressure chamber is V2 larger than V1, the actuator changing from the first state to the second state and then returning to the first state to eject ink from the ejection port,a proper oscillation period Ts of an oscillation generated by integral deformation of the actuator and the pressure chamber when ink is ejected from the ejection port, and a proper oscillation period Td of ink filling up a first partial passage in the individual ink passage leading from an outlet of the pressure chamber to the ejection port, satisfying a condition that Ts/Td is not less than 0.36 and not more than 0.90; or not less then 1.1 and not more than 1.7.

2. The head according to claim 1, wherein Ts and Td satisfy a condition that Ts/Td is not less than 0.36 and not more than 0.48; not less and 0.60 and not more than 0.90; or not less than 1.1 and not more than 1.7.

3. The head according to claim 1, wherein Ts, Td, and a proper oscillation period Tc of ink filling up the whole of the individual ink passage, satisfy a condition that Ts×Td/Tc2 is not less than 0.0060 and not more than 0.014.

4. The head according to claim 1, wherein the area of a section of the first partial passage, which leads from the outlet of the pressure chamber to the ejection port, perpendicular to a longitudinal axis of the first partial passage in a region of the first partial passage, is larger than either of the area of a boundary between the first partial passage and the pressure chamber and the area of the ejection port.

5. The head according to claim 1, wherein the area of a section of a second partial passage in the individual ink passage, which leads from the outlet of the common ink chamber to the pressure chamber, perpendicular to a longitudinal axis of the second partial passage in a region of the second partial passage, is smaller than either of the area of a boundary between the second partial passage and the pressure chamber and the area of the outlet of the common ink chamber.

6. The head according to claim 1, wherein the actuator comprises an individual electrode opposed to the pressure chamber; a piezoelectric layer having a region opposed to the pressure chamber; and a common electrode cooperating with the individual electrode to sandwich the region of the piezoelectric layer.

7. The head according to claim 6, wherein the actuator takes the first state when the voltage between the individual electrode and the common electrode has a first value not equal to zero, and the actuator takes the second state when the voltage between the individual electrode and the common electrode has a second value smaller than the first value.

8. The head according to claim 6, wherein the individual electrode and the common electrode sandwich only one piezoelectric layer.

9. The head according to claim 6, wherein either of the pressure chamber and the individual electrode has a shape, in a plan view, that is long along one axis and tapered in both directions along the axis from the center of the axis.