Patent Grant
7156480
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-201719, filed Jul. 25, 2003, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an ink-jet head driving method and an ink-jet recording apparatus in which an ink drop is ejected from a nozzle by varying the capacity of a pressure chamber that contains ink.
2. Description of the Related Art
With the above configuration, when the piezo-electric actuator 7 is driven, the pressure generating chambers 2 are vibrated. This vibration varies the capacity of the chambers 2 to eject an ink drop 4 from the nozzle 5. The ink drop 4 reaches a recording medium such as recording paper and forms a dot thereon. If such dots are formed in sequence, given characters, images, etc., which correspond to image data, are printed on the recording medium.
In the ink-jet recording head 1 described above, an ink drop needs ejecting with stability to correctly print characters and images on a recording medium based on input printing information.
However, the actual use of the ink-jet recording head 1 for printing may cause a problem in which an ink drop is ejected unstably due to various factors and thus a desired printing result cannot be obtained. One of the factors is evaporation of volatile components from ink.
More specifically, ink used for ink-jet recording employs water as the main solvent, and coloring such as various kinds of organic solvent dye such as a surface-active agent is added to the water. If no ink drops for some long period of time, moisture is drawn from an opening of the nozzle 5 that is exposed to outside air. The ink therefore increases in viscosity or partly solidifies to block the nozzle 5.
The above problem is resolved as follows. The ink-jet recording head 1 moves away from a printing area and ink is discharged from the ink chamber 9, or ink is discharged from the nozzle 5 by forcibly sucking new ink through the nozzle 5 by means of a pump.
In order to eject ink from the nozzle 5 for high-quality printing with stability, however, the above operation has to be performed frequently. This causes the following problem. An amount of ink consumed increases and so do printing costs, and a large amount of ejected ink should be disposed of.
As a method of resolving the above problem, for example, Jpn. Pat. Appln. KOKAI Publications Nos. 57-61576 and 9-29996 disclose an operation of providing a pressure generating chamber with such a small vibration that no ink drops jump out of the nozzle even when no ink drops are ejected from the nozzle (this operation is called a precursor).
There now follows an explanation as to the precursor referring to
In order to perform the precursor, a driving voltage that is lower than that for ejecting a normal ink drop has to be applied. Another driving power supply is required accordingly.
Although the above operation (precursor) is effective if no ink drop is ejected for a short period of time, it simply decreases the speed at which the viscosity of ink increases because the ink 11 in the nozzle 5 is not replaced with a new one. If, therefore, no ink drop is ejected for a long period of time, the ink 11 will solidify in the nozzle 5, which makes it difficult or impossible to eject an ink drop again.
When the very small vibration changes the meniscus from a convex to a concave as shown in
For example, Jpn. Pat. Appln. KOKAI Publication No. 9-29996 described above discloses a method including a step (precursor) of providing such a small vibration that no ink drops jump out of the nozzle even when no ink drops are ejected from the nozzle and a step of retreating the ink-jet recording head from a printing area in a fixed period of time and ejecting the ink 11 from the pressure generating chamber 2 and from near the opening of the nozzle 5 (hereinafter referred to as a spit operation). The spit operation requires its own driving voltage waveform whose potential difference is greater than that of a driving voltage waveform used for normal printing, and a large amount of ink 11 is ejected from the pressure generating chamber 2 and replaced with a new one, thereby preventing ink from solidifying and increasing in viscosity for a long period of time.
The method of the Publication necessitates a driving waveform exclusively for the spit operation, and the driving waveform requires three different waveforms of a normal ejecting waveform, a precursor driving waveform and a spit driving waveform. The number of driving power supplies therefore increases to make a driving circuit complicated and thus make the ink-jet recording apparatus expensive.
If the ink-jet recording apparatus turns off and sits idle for a long period of time without performing any precursor or spit operation, the ink 11 remaining near the nozzle 5 increases in viscosity and easily solidifies.
In an ink ejecting operation prior to a printing operation, too, ink that increases in viscosity is attached to the periphery of the nozzle 5 of the nozzle plate 3, as is a coagulation of solidified ink, thereby shifting the ink ejecting direction.
An object of the present invention is to provide an ink-jet head driving method and an ink-jet recording apparatus each capable of preventing ink that increases in viscosity and a coagulation of solidified ink from attaching to the periphery of a nozzle.
According to an aspect of the present invention, there is provided an ink-jet head driving method of an ink-jet recording apparatus including a pressure chamber that contains ink, a nozzle communicating with the pressure chamber, which ejects the ink from the pressure chamber, an ink-jet head having an actuator that increases and decreases a capacity of the pressure chamber, and a driving signal generation unit that supplies the actuator with a driving signal to eject an ink drop from the nozzle, the method comprising supplying the actuator with a very low pressure driving signal to increase the capacity of the pressure chamber and then return the increased capacity to an original size when no ink is ejected from the nozzle, a pulse width of the very low pressure driving signal being about twice as long as a pressure propagation time period during which a pressure wave in the ink propagates through the pressure chamber.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.
Embodiments of the present invention will now be described with reference to the accompanying drawings.
The ink-jet head 21 includes a common pressure chamber 36 communicating with each of the pressure chambers 31. The common pressure chamber 36 is supplied with ink from ink supply means (not shown) through an ink supply inlet 37. The pressure chambers 31 and nozzle 33 as well as the common pressure chamber 36 are filled with ink. If the pressure chambers 31 and nozzle 33 are filled with ink, a meniscus is formed in the nozzle 33.
In
The driving signal generation means 22 includes a circuit that generates a driving pulse for ink ejection and a driving pulse for a precursor as a very low pressure driving signal. This circuit will now be described with reference to
The MOSFETs Q1 and Q4 turn on for a period of time Ta and the MOSFETs Q2 and Q3 turn off for a period of time Ta to generate an expanded pulse p1 shown in
The MOSFETs Q1 and Q4 turn on for a period of time 2Ta and the MOSFETs Q2 and Q3 turn off for a period of time 2Ta to generate an expanded pulse p1 of −Vcc shown in
In
When a voltage of −Vcc is applied between electrodes of the piezoelectric member 35 for a period of time Ta, the member 35 is deformed to increase the capacity of the pressure chambers 31 and thus the pressure chambers 31 generate a negative pressure. This pressure is inverted to a positive pressure as shown in
When time 2Ta elapses, the pressure in the pressure chambers 31 changes from a positive to a negative and then a positive. If the voltage between electrodes of the piezoelectric member 35 returns to zero during the lapse of time 2Ta, the pressure in the pressure chambers 31 becomes negative and the phase of the pressure wave is reversed. Accordingly, the amplitude of the pressure wave decreases and so does the vibration of the residual pressure.
As described above, the nozzle 33 ejects ink if the driving signal generation means 22 generates a driving pulse q for ink ejection as shown in
When a voltage of −Vcc is applied between electrodes of the piezoelectric member 35, the member 35 is deformed to increase the capacity of the pressure chambers 31. The pressure chambers 31 thus generate a negative pressure and the meniscus in the nozzle 33 retreats toward the pressure chambers 31 (
As described above, the capacity of the pressure chambers 31 increases and returns to its original size such that the meniscus does not change to a convex on the surface of the nozzle plate 30 by the driving pulse q for the precursor. The time required for returning the capacity is set twice as long as the pressure propagation time Ta. Therefore, the capacity of the pressure chambers 31, which increases when the pressure in the chambers 31 is negative, returns to its original size. The pressure vibration is attenuated and the convex of the meniscus of reacting ink is minimized as illustrated in
With the above operation, the driving pulse q for the precursor can prevent ink from attaching and remaining on the surface of the nozzle plate 30 near the nozzle 33. The ejecting direction of ink drops can thus be prevented from shifting to thereby achieve stable, high-quality printing.
The driving pulse for a precursor and that for ink ejection are generated by the same driving power supply Vcc. The costs for the ink-jet recording head apparatus can thus be lowered with a simple configuration of the driving circuit.
The driving period Tc of a driving pulse for a precursor shown in
If Tc is considerably longer than Tb, the ink-jet recording apparatus can decrease in power consumption when it stands by for printing.
Even though a driving pulse for a precursor is applied between electrodes of the piezoelectric member 35 a given number of times, ink in the nozzle 33 is likely to increase in viscosity when nonprinting time is longer than a certain period of time.
In the above case, a spit operation is periodically performed to discharge the ink that increases in viscosity in a nonprinting area. The driving circuit shown in
As described above, the spit operation is performed when nonprinting time is longer than a certain period of time. It is thus possible to prevent ink from attaching and remaining on the surface of the nozzle plate near the nozzle. Consequently, it is possible to prevent the ejecting direction of ink drops from shifting, thereby achieving stable, high-quality printing.
The driving power supply of a driving pulse in the spit operation is the same as the power supply Vcc of both the driving pulse for a precursor and that for ink ejection. The arrangement of the driving circuit can be simplified to lower the costs for the ink-jet recording apparatus.
When the apparatus turns off and sits idle for a long period of time, ink in the nozzle 33 considerably increases in viscosity or solidifies. No advantages can thus be obtained even using the same driving pulse as those for the precursor and spit operations described above.
In order to resolve the above problem, an ink-jet recording apparatus according to a second embodiment of the present invention will now be described with reference to
Assume that the ink-jet recording apparatus with the above configuration turns off and sits idle for a long period of time and ink in the nozzle 33 considerably increases in viscosity or solidifies. First, the pump 43 is driven in the backward direction to cause ink to flow from the nozzle 33 in the direction of arrow a through the tube 42. The ink is agitated in a pressure chamber 31. Then, the pump 43 is driven in the forward direction to discharge ink from the pressure chamber 31 through the nozzle 33 and supply a new ink into the pressure chamber 31 from the pressure chamber 31 in the ink bottle 44.
The above operation makes it possible to prevent ink that increases in viscosity and a coagulation of solidified ink from attaching and remaining on the surface of the nozzle plate near the nozzle. Consequently, the ejecting direction of ink drops can be prevented from shifting to thereby achieve stable, high-quality printing.
When the pump 43 causes ink to flow backward from the nozzle 33 to the pressure chamber 31 and agitate it therein, a cap can be put on the nozzle plate to apply a positive pressure.
A driving pulse for a precursor can be generated from the driving signal generation means 22 to return ink to the pressure chamber 31 from the nozzle 33 and agitate the ink while slightly oscillating the pressure chamber 31.
In the above embodiments, the driving period Tc of a driving pulse for a precursor is about ten times as long as the driving period Tb of a driving pulse for ink ejection. However, the embodiments are not limited to this.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-201719 | Jul 2003 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5764247 | Asai | Jun 1998 | A |
| 5980034 | Tsai et al. | Nov 1999 | A |
| 6106092 | Norigoe et al. | Aug 2000 | A |
| 6109716 | Takahashi | Aug 2000 | A |
| 6123405 | Temple et al. | Sep 2000 | A |
| 6193343 | Norigoe et al. | Feb 2001 | B1 |
| 6231174 | Haigo | May 2001 | B1 |
| 6378973 | Kubota et al. | Apr 2002 | B1 |
| 6409295 | Norigoe | Jun 2002 | B1 |
| 20040041871 | Davis et al. | Mar 2004 | A1 |
| Number | Date | Country |
|---|---|---|
| 0 652 106 | May 1995 | EP |
| 652106 | May 1995 | EP |
| 0 751 873 | Nov 1998 | EP |
| 57-61576 | Apr 1982 | JP |
| 9-29996 | Feb 1997 | JP |
| 2001-26107 | Jan 2001 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20050018003 A1 | Jan 2005 | US |
