INKJET RECORDING APPARATUS AND METHOD OF DETERMINING CONTROL CONDITION IN THE APPARATUS

Abstract

An actuator can selectively switch a volume of a pressure chamber between a first state V1 and a second state V2, which is greater than V1. The actuator changes from the first state into the second state and then changes back into the first state to eject ink from an ejection port. A controller controls the actuator such that To/Tc falls within a range from 0.51 to 0.54. To represents the time period between time the actuator starts to change from the first state into the second state, to a time the actuator starts to change from the second state into the first state. Tc represents the period of proper oscillation of ink filling up the individual ink passage. The actuator is controlled so that a variation in ink ejection speed is prevented from being too large relative to the variation in the degree of deformation of the actuator.

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. 8A, 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;

FIG. 9 is a graph showing a relation of the ejection speed of ink droplets ejected from a nozzle when a voltage pulse corresponding to FIG. 7 is supplied to an individual electrode, to To/Tc, where To represents the pulse width;

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;

FIGS. 11A and 11B are graphs showing results of numeric analysis performed by using the model shown in FIGS. 10A to 10C; and

FIG. 12 is a flowchart showing a series of steps for determining a condition for controlling an inkjet head of the embodiment, on the basis of the analysis by the inventors of the present invention.

Claims

1. An inkjet recording apparatus comprising: a passage unit comprising a common ink chamber and an individual ink passage leading, from an outlet of the common ink chamber via a pressure chamber to an ink ejection port;an actuator that can selectively take a first state in which the volume of the pressure chamber is V1 and a second state in which the volume of the pressure chamber is V2 larger than V1; anda controller that controls the actuator to change from the first state into the second state and then change back into the first state to eject ink from the ejection port, the individual ink passage being formed so as to satisfy both of the following conditions:(a) a curved line representing a change in the ejection speed of ink to be ejected from the ejection port, relative to a change in the time period To from a time point at which the actuator starts to change from the first state into the second state, to a time point at which the actuator starts to change from the second state into the first state, when the actuator changes from the first state into the second state and then changes back into the first state to eject ink from the ejection port, has a general shape being convex in the direction of the ejection speed increasing; and(b) the ink ejection speed takes at least one maximal value on the curved line in a region in which To is larger than ½ times the period Tc of proper oscillation of ink filling up the individual ink passage,the controller controlling the actuator such that the value of To/Tc falls within a range from 0.51 to 0.54.

2. The apparatus according to claim 1, wherein the common ink chamber and the pressure chamber are opposed to each other, and the ejection port is formed on an ejection face of the passage unit, which face is disposed on the opposite side of the common ink chamber from the pressure chamber.

3. The apparatus according to claim 1, wherein the area of a section of a region of a first partial passage of the individual ink passage leading from an outlet of the pressure chamber to the ejection port, perpendicular to a longitudinal axis 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.

4. The apparatus according to claim 1, wherein the area of a section of a region of a second partial passage of the individual ink passage leading from the outlet of the common ink chamber to the pressure chamber, perpendicular to a longitudinal axis 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.

5. A method of determining a control condition in an inkjet recording apparatus comprising a passage unit comprising a common ink chamber and an individual ink passage leading from an outlet of the common ink chamber via a pressure chamber to an ink ejection port; an actuator that can selectively take a first state in which the volume of the pressure chamber is V1 and a second state in which the volume of the pressure chamber is V2 larger than V1; and a controller that controls the actuator to change from the first state into the second state and then change back into the first state to eject ink from the ejection port, the individual ink passage being formed so as to satisfy the following condition: (a) a curved line representing a change in the ejection speed of ink to be ejected from the ejection port, relative to a change in the time period To from a time point at which the actuator starts to change from the first state into the second state, to a time point at which the actuator starts to change from the second state into the first state, when the actuator changes from the first state into the second state and then changes back into the first state to eject ink from the ejection port, has a general shape being convex in the direction of the ejection speed increasing; and(b) the ink ejection speed takes at least one maximal value on the curved line in a region in which To is larger than ½ times the period Tc of proper oscillation of ink filling up the individual ink passage,the method comprising a condition determining step of determining a control condition for the controller controlling the actuator such that To is longer than ½ times the period Tc of proper oscillation of ink filling up the individual ink passage, and causes the ink ejection speed not to take the maximal value on the curved line.