Patent Application
20060284911
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-176463, filed Jun. 16, 2005, 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 driving apparatus for changing the capacity of a pressure chamber in which ink has been filled by a piezoelectric element in response to a print signal, and then, ejecting an ink droplet from a nozzle which communicates with the pressure chamber by the resulting pressure change, thereby printing a character or an image and the like on a printing medium.
2. Description of the Related Art
A description will be given with a conventional print head with reference to
In general, in an ink jet printer, in the case where high quality printing is carried out, there is used an area gradation system such as a dither system, for forming one pixel by producing a matrix with a plurality of dots without changing the size of an ink droplet, and expressing gradation based on a difference in the number of dots in pixel. In this case, resolution must be sacrificed in order to allocate a certain number of gradations. In addition, there is provided a density gradation system for changing the density of one dot by varying the size of an ink droplet. In this case, although resolution is not sacrificed, there is a problem that a technique for controlling the size of an ink droplet is difficult.
Further, there is a so called multi-drop driving system for carrying out density gradation by varying the number of ink droplets to be printed with respect to one dot without changing the size of an ink droplet. In this case, resolution is not sacrificed, and there is no need to control the size of an ink droplet, thus making it possible to comparatively easily carry out this driving system.
A method for driving an ink jet head in a multi-drop system is also known (refer to Jpn. Pat. No. 2931817). Further, an ink jet type printing apparatus is known as reducing a cycle of a drive signal so as to speed up printing (refer to Jpn. Pat. Appln. KOKAI Publication No. 2001-146003). Furthermore, an ink jet printing apparatus for, when a repetition time for ejecting ink droplets variously changes, efficiently ejecting a predetermined amount of ink from an ejecting port is also known (refer to Jpn. Pat. Appln. KOKAI Publication No. 2000-177127).
In this multi-drop driving system, in the case where a plurality of liquid droplets are continuously ejected, an ejection speed of second and subsequent droplets can be increased more significantly than that in a first liquid droplet by using residual pressure vibration of the droplets just ejected before.
On the other hand, in general, the first liquid droplet becomes lower in ejection speed than the second and subsequent liquid droplets because a pressure vibration is applied in a state in which meniscus is stationary. Thus, there is a problem that ejection becomes unstable or print quality is degraded because of a small amount of ejection.
In order to avoid such a problem, there is an option for increasing an applied voltage, and then, increasing a pressure vibration entirely applied to a pressure chamber, thereby increasing a first-drop ejection speed. However, there is a problem that power consumption is increased, and a heating rate is increased by increasing a voltage. In addition, there is a problem that ejection becomes unstable because the ejection speed of the second and subsequent droplets becomes too high or print quality is degraded due to displacement in ink deposition between gradations, resulting from the increased difference in ejection speed of each droplet.
In addition, another method for avoiding a problem that an amount of ejection is small and print quality is degraded includes increasing a first-drop ejection speed by applying a fine pressure vibration to an extent that a liquid droplet is not ejected before a first-drop drive pulse (hereinafter, such a drive pulse is referred to as a boost pulse). This boost pulse is redundantly applied, whereby a time of an entire drive cycle is extended, and therefore, such an extended time is disadvantageous for high speed printing.
It is an object of the present invention to provide an ink jet head driving method and driving apparatus which is capable of improving unstable ejection or degraded print quality in the case where the number of liquid droplets is small and which is capable of achieving printing at a high speed in the case where the number of liquid droplets is large.
According to one aspect of the present invention, there is provided an ink jet head driving method for applying a drive pulse to an actuator to change capacities of a plurality of pressure chambers in which ink has been filled, ejecting an ink droplet from a nozzle formed in communication with the pressure chamber to print onto a printing medium, and moreover, continuously ejecting a plurality of liquid droplets to carry out gradation printing according to the number of liquid droplets, the method comprising: making control so as to, in the case where the number of the liquid droplets is smaller than a predetermined number, apply a boost pulse to amplify a pressure vibration of the pressure chamber prior to a drive pulse for ejecting a first liquid droplet; and in the case where the number of liquid droplets is equal to or greater than the predetermined number, disable applying of the boost pulse.
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.
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
In
A common pressure chamber 36 communicating with each of the pressure chambers 31 is formed at the ink jet head 1. To this common pressure chamber 36, ink is injected from ink supply means (not shown) via an ink supply port 37 so as to fill the ink in the common pressure chamber 36, each pressure chamber 31, and nozzle 33. When the ink is filled in the pressure chamber 31 and the nozzle 33, whereby ink meniscus is formed in the nozzle 33.
Now, a detailed construction of the drive signal generating means 2 will be described with reference to
The number “n” of drive pulses outputted from this drive pulse number generating section 41 is sent to a judging section 42, and it is judged that the number “n” of drive pulses is equal to or greater than a predetermined number N (for example, N=4).
Here, a value of a predetermined number N stored in advance in this judging section 42 is in the range of 1≦N≦n. This value can be arbitrarily changed externally from an operating panel of an ink jet printing apparatus or a controller or the like of a host computer.
A judgment result obtained by this judging section 42 is output to a drive sequence generating section 43. Here, the number “n” of drive pulses generated by the drive pulse number generating section 41 is also input to the drive pulse sequence generating section 43.
The drive sequence generating section 43 controls waveform selection at a waveform selecting section 44. To this waveform selecting section 44, there are input: a drive pulse Pd output from a drive pulse waveform generating section 45 (refer to
In the drive sequence generating section 43, in the case where the number “n” of drive pulses is smaller than a predetermined number N (for example, N=4), namely, the number 3 or less, the waveform output section 47 controls the waveform selecting section 44 so as to select and output the drive pulse Pd “n” times after the boost pulse Pb is selected once.
On the other hand, in the case where the number “n” of drive pulses is equal to or greater than a predetermined number N (for example, N=4), namely, the number is 4 or more, the drive sequence generating section 43 controls the waveform selecting section 44 so as to select and output the drive pulse Pd “n” times.
The waveform output from this waveform selector 44 is output to drive output means 48 described in detail with reference to
When the boost pulse Pb from the drive signal generating means 2 is applied to the piezoelectric member 35 of the actuator ACT, meniscus is vibrated to an extent that no ink droplet is ejected.
When the drive pulse Pd from the drive signal generating means 2 is applied to the piezoelectric member 35, this piezoelectric member 35 displaces the vibration plate 34 and changes the capacity of the pressure chamber 31, whereby a pressure wave is generated in the pressure chamber 31, and an ink droplet is ejected from the nozzle 33.
Now, referring to
In a multi-drop driving system, this drive pulse Pd is continuously generated by the number of liquid droplets to be ejected. In the present embodiment, all the drive pulses of each drop are formed in the same shape without being limited thereto.
Here, when a pressure propagation time is defined as Ta when a pressure wave in ink propagates the inside of the pressure chamber from a common pressure chamber at a rear end to a nozzle tip end, the power conducting time t1 of the expansion pulse p1 is set in the proximity of Ta; and the power conducting time t2 of the contraction pulse p2 is set in the range of 1.5 Ta to 2 Ta. In addition, the pause time t3 is set in the range of 0 to Ta.
Now, referring to
First, when a voltage −Vaa is applied between electrodes of the piezoelectric member 35, the piezoelectric member 35 is deformed so as to rapidly increase the capacity of the pressure chamber 31 so that a negative pressure is momentarily generated in the pressure chamber 31. This pressure is inverted to a positive pressure when a pressure propagation time Ta has elapsed.
Next, when a voltage +Vaa having opposite polarity is applied between electrodes of the piezoelectric member 35, the piezoelectric member 35 is deformed so as to rapidly contract the capacity of the pressure chamber 31 from the expanded state, whereby a positive pressure is momentarily generated in the pressure chamber 31. The pressure wave generated by this pressure coincides with a first generated pressure wave in phase so that the amplitude of the pressure wave is rapidly increased. At this time, an ink droplet is ejected from a nozzle.
Then, when the time 2 Ta which is twice the pressure propagation time has elapsed, the pressure in the pressure chamber 31 changes in a direction from positive to negative, and then, positive. At this time, the voltage between the electrodes of the piezoelectric member 35 is reset to zero, whereby the contracted capacity of the pressure chamber reverts to its original state, and the pressure in the pressure chamber 31 momentarily decreases. Thus, the amplitude of the pressure wave is weakened, and then, the residual pressure vibration decreases.
Further, when the pause time Ta has elapsed the pressure vibration during this period changes in a direction from positive to negative. At this time, when the second-drop expansion pulse p1 is continuously applied, the capacity of the pressure chamber 31 is rapidly increased again, and a negative pressure is momentarily applied again in the pressure chamber 31. At this time, the next pressure vibration is applied in a state in which the residual pressure vibration of the first drop still remains. Thus, the pressure in the pressure chamber 31 is obtained as a negative pressure which is greater than the case of the first drop.
Therefore, when the next pressure propagation time Ta has elapsed, the inverted positive pressure also increases. Further, the contraction pulse p2 is applied, whereby a pressure required for-the second-drop ejection becomes greater than that required for the first-drop. Here, the pause time t3 is set to a proper time, whereby a value of the residual vibration can be changed. An ejection speed can be increased or decreased by increasing the pressures required for the second-drop ejection more significantly than the first-drop.
In general, a drive voltage can be reduced more significantly, enabling efficient driving by making control such that the second-drop pressure is increased more significantly than the first-drop pressure.
Now, referring to
The boost pulse Pb consists of a contraction pulse Bp for contracting the capacity of the pressure chamber 31 and a pause time Bt2, and the contraction pulse Bp is produced as a rectangular wave having a voltage amplitude of +Vaa when a power conducting time is Bt1. The succeeding first drop and subsequent pulses Pd are identical to those shown in
In addition, when the pressure propagation time is set to Ta, the power conducting time Bt1 of the contraction pulse Bp is set to 2 Ta, and the pause time Bt2 is set in the order of 2 Ta.
In the present embodiment, although the form of the boost pulse Pb has the contraction pulse Bp and the pause time Bt2, the contraction pulse may be an expansion pulse and the pause time may be eliminated without being limited thereto.
Now, referring to
When a voltage +Vaa is applied between the electrodes of the piezoelectric member 35 by means of the boost pulse Pb, the piezoelectric member 35 is deformed so as to rapidly contract the capacity of the pressure chamber 31. Thus, a positive pressure is momentarily generated in the pressure chamber. This pressure changes in a direction from positive to negative, and then, to positive while a time 2 Ta has elapsed. Next, the voltage between the electrodes of the piezoelectric member 35 is reset to zero, whereby the capacity of the pressure chamber 31 reverts to its original state rapidly. Thus, the pressure in the pressure chamber is momentarily inverted in phase from positive to negative.
Then, while the pause time 2 Ta has elapsed, the pressure changes in a direction from negative to positive, and then, to negative in turn. When a voltage −Vaa is applied between the electrodes of the piezoelectric member 35 by means of the first-drop expansion pulse p1, the piezoelectric member 35 is deformed so as to rapidly increase the capacity of the pressure chamber 31. Thus, a negative pressure is momentarily applied to the inside of the pressure chamber 31.
At this time, the residual pressure vibration caused by the boost pulse Pb still remains in the pressure chamber 31, and thus, greater pressure amplitude is produced as compared with a case in which no boost pulse Pb is applied. Therefore, when next pressure propagation time Ta has elapsed, the inverted positive pressure also increases. Further, a voltage +Vaa is applied between the electrodes of the piezoelectric member 35 by means of the contraction pulse p2, and the piezoelectric member 35 is deformed so as to rapidly contract the capacity of the pressure chamber 31 from its expanded state, whereby a positive pressure is momentarily applied in the pressure chamber 31. Further, the pressure amplitude increases more significantly than a case in which no boost pulse Pb is applied. The boost pulse Pb is thus applied, whereby a pressure required for the first-drop ejection can be increased by the residual pressure vibration.
As shown in
In the meantime, in the case where the number “n” of drive pulses is smaller than a predetermined number N (n<N), namely, the number is 3 or less, the drive signal generating means 2 selects the boost pulse Pb one time, and then, outputs the drive pulse Pd to the actuator ACT by “n” times.
On the other hand, in the case where the number “n” of drive pulses is equal to or greater than a predetermined number N (n≧N), namely, the number is 4 or more, the drive signal generating means 2 selects and outputs the drive pulse Pd to the actuator ACT by “n” times.
In one to three drops in which the number of liquid droplets is smaller than the predetermined number N=4, the boost pulse Pb is applied prior to the drive pulse Pd. In four to seventh drops in which the number of liquid droplets is equal to or greater than the predetermined number N=4, a relationship between the number of drops and an ejection speed in the case where no boost pulse Pb is applied is obtained as shown in
In the present embodiment, the maximum number of liquid drops is 7, and the predetermined number is set to N=4, whereby one to three drops have been set to apply the boost pulse Pb. However, the present invention is not limited to this embodiment.
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 |
|---|---|---|---|
| 2005-176463 | Jun 2005 | JP | national |
