JP2004009548A - Driving method of inkjet head and inkjet printer - Google Patents

Abstract

A method of driving an ink-jet head capable of increasing the printing speed when performing one-pixel printing of a predetermined density by discharging ink droplets a plurality of times and finely expressing the gradation of the density in multiple steps.
An ink jet head drive control device (1) for an ink jet printer has different densities by discharging once or twice a small mass ink droplet and once or twice discharging a large mass ink droplet. Perform one-pixel printing. Compared to the case where one pixel printing of the same density is performed by discharging ink droplets of the same mass, the number of times of discharging ink droplets can be reduced and the printing speed can be increased, and at the same time, the density can be finer and multi-step. Can be changed.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of driving an ink jet head and an ink jet printer for forming a print of one pixel by ejecting ink droplets one or more times in order to obtain a predetermined print density or the like, and in particular, to print in more steps. The present invention relates to a method for driving an ink jet head capable of changing a density and increasing a printing speed, and an ink jet printer.
[0002]
[Prior art]
As a printing method using an ink-jet head, there is known a method in which printing is performed in a print mode in which ink droplets are ejected to a print area of one pixel a plurality of times for the purpose of increasing a recording density or the like. For example, Japanese Patent Publication No. 4-48626, Japanese Patent No. 3219514, and the like disclose a method of ejecting a plurality of ink droplets to one pixel region, and overprinting a plurality of ink droplets with their positions shifted from each other by a predetermined amount. There has been proposed an ink jet recording apparatus for increasing the recording density. In addition, the latter patent publication has a recording head that discharges a large amount of ink droplets and a recording head that discharges a small amount of ink droplets. Discloses a method of performing high-resolution and high-density printing by over-strike of ink droplets using a recording head that discharges ink droplets.
[0003]
Various types of ink jet heads can be used as an ink jet head used to perform printing by ejecting ink droplets a plurality of times to the area of one pixel. For example, ink that stores ink using electrostatic force can be used. An electrostatically driven ink jet head that discharges ink droplets by changing the volume of the chamber can be used. As the electrostatic drive type ink jet head, for example, those described in JP-A-6-71882, JP-A-6-55732, and JP-A-5-50601 are known.
[0004]
[Problems to be solved by the invention]
When printing is performed for one pixel by discharging ink droplets a plurality of times using a conventional inkjet head, an inkjet head that discharges a small amount of ink droplets in order to perform high-density printing at high recording density , It is necessary to discharge ink droplets many times. Accordingly, when high-density printing is performed, the number of ejections of ink droplets increases, and the printing speed decreases accordingly. In order to increase the printing speed, it is necessary to increase the drive frequency that regulates the ejection cycle of the inkjet head. However, since the drive frequency naturally has an upper limit, one pixel can be used for multiple times of ink droplets. In the case of adopting the printing mode formed by ejection, the printing speed is sacrificed to maintain a high recording density, and the recording density must be sacrificed to increase the printing speed.
[0005]
Further, conventionally, one-pixel printing with different densities is performed by ejecting ink droplets of the same mass a plurality of times, so that the gradation expression is based on the ejection mass of ink droplets per ejection. It will change step by step. Therefore, finer gradation expression cannot be performed.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide a method of driving an ink-jet head capable of increasing the printing speed in such a printing mode by reducing the number of ejections of ink droplets necessary for one-pixel printing when performing high-density printing. It is to propose.
[0007]
Another object of the present invention is to propose a method of driving an ink-jet head and an ink-jet printer capable of performing finer gradation expression in addition to the above-described problems.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the present invention relates to a method for driving an ink jet head that forms printing of one pixel by discharging ink droplets one to plural times.
The mass of ink droplets ejected from the same ink nozzle is made variable,
The printing of the one pixel is performed by discharging a predetermined mass of ink droplet from the ink nozzle at least once.
[0009]
In the inkjet head driving method according to the present invention, the mass of ink droplets ejected from the same ink nozzle is changed. Therefore, when one pixel is printed at a predetermined density, the number of times of discharging ink droplets can be reduced as compared with the case where printing is performed at a predetermined density by discharging only small ink droplets. Therefore, the printing speed can be increased without increasing the driving frequency of the inkjet head. Further, it is possible to more finely express the gradation of the density as compared with the case where the ink droplets having the same mass are ejected.
[0010]
In order to reduce the number of ejections of ink droplets in one-pixel printing of a predetermined density, the ejection mass of ink droplets ejected from the ink nozzles can be changed in at least two stages, and the ink required for printing of one pixel can be changed. The combination of the number of ejections of ink droplets and the ejection mass of each ink droplet may be determined so that the mass can be obtained with the minimum number of ejections of ink droplets by the ink nozzle.
[0011]
In addition, when printing is performed while the ink jet head and the recording medium are relatively moved, in order to form a united print of one pixel by discharging ink droplets a plurality of times, a predetermined minimum drive is required. It is desirable to eject ink droplets continuously in a cycle.
[0012]
Next, the method of driving an ink jet head of the present invention can be applied to an electrostatic drive type. An electrostatically driven ink jet head, a plurality of the ink nozzles, an ink pressure chamber communicating with each ink nozzle, and a vibrating plate that can vibrate in an out-of-plane direction forming a part of each ink pressure chamber, A counter electrode disposed opposite to each of the diaphragms; a driving voltage pulse is applied between the diaphragm and the counter electrode to deform the diaphragm so that ink is supplied from the ink nozzles; This is to discharge droplets.
[0013]
In this case, the ejection mass of the ink droplet ejected from the ink nozzle can be changed by applying the drive voltage pulse having a different waveform between the diaphragm and the counter electrode.
[0014]
Further, the gap between the diaphragm and the counter electrode is changed in two or more stages, and a small mass ink droplet is ejected from the ink nozzle by deformation of a portion of the diaphragm corresponding to a narrow gap portion, and the gap is widened. Due to the deformation of the portion of the vibration plate corresponding to the gap, a large amount of ink droplet can be ejected from the ink nozzle.
[0015]
In addition to or instead of the gap between the electrodes, a flexible portion and a non-flexible portion are formed on the diaphragm, and a small-mass ink droplet is ejected from the ink nozzle by deformation of the flexible portion. Then, a large-mass ink droplet can be ejected from the ink nozzle by deformation of the hardly bent portion.
[0016]
Also, a combination of the number of times of ink droplet ejection and the mass of each ink droplet ejected is such that the amount of ink required for printing for one pixel can be obtained with the minimum number of times of ink droplet ejection by the ink nozzle. Is desirable.
[0017]
Further, when printing is performed while the ink jet head and the recording medium are relatively moved, in order to form a united one-pixel print by discharging ink droplets a plurality of times, continuous printing is performed at a predetermined minimum drive cycle. It is desirable that the ink droplets be ejected.
[0018]
In this case, it is preferable that the drive voltage pulse be applied between the diaphragm and the counter electrode such that the direction of current application is alternately reversed. By performing such forward / reverse alternating current, the accumulation of residual charges between the electrodes can be suppressed, so that an appropriate ink droplet ejection operation can be guaranteed.
[0019]
Further, in order to perform the forward / reverse alternating current evenly, it is desirable to perform the following. In other words, when the driving voltage pulse having a small waveform and / or the driving voltage pulse having a large waveform is applied a plurality of times for printing the one pixel, the driving voltage pulse having an even number of small waveforms is applied. It is desirable to apply a voltage pulse and / or an even number of large waveform drive voltage pulses.
[0020]
Next, the present invention relates to an ink-jet printer, wherein one pixel is printed by the above-described method of driving an ink-jet head. According to the present invention, it is possible to increase the printing speed when printing one pixel by discharging ink droplets a plurality of times, and it is possible to express finer density.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an inkjet printer to which the present invention is applied will be described with reference to the drawings.
[0022]
(overall structure)
FIG. 1 is a schematic configuration diagram showing a main part of the ink jet printer of the present embodiment. The ink jet printer of this example is of a serial type, and has an electrostatically driven ink jet head 4 mounted on a carriage 3 that can reciprocate along a guide shaft 2. The ink is supplied to the ink-jet head 4 from the ink tank 5 disposed at a fixed position via a flexible ink tube 6. A platen roller 7 is arranged parallel to the guide shaft 2 and moves on the surface of the recording medium 8 conveyed along the surface in the main scanning direction Y while moving in the sub scanning direction X orthogonal to the main scanning direction Y. Printing is performed by the inkjet head 4.
[0023]
(Inkjet head)
FIG. 2 is a sectional view of the ink jet head 4, FIG. 3 is a plan view thereof, and FIG. 4 is a partial sectional view thereof.
[0024]
As shown in these figures, the ink jet head 4 has a silicon substrate 42 sandwiched therebetween, a nozzle plate 43 also made of silicon on the upper side, and a borosilicate glass substrate 44 having a thermal expansion coefficient close to that of silicon on the lower side. It has a three-layer structure. By etching the central silicon substrate 42 from the surface thereof, a plurality of independent, for example, five ink chambers 45, one common ink chamber 46, and this common ink chamber 46 communicate with each ink chamber 45. The grooves functioning as the respective ink supply paths 47 are formed. These grooves are closed by the nozzle plate 43, and the respective portions 45, 46, 47 are defined.
[0025]
In the nozzle plate 43, ink nozzles 48 are formed at positions corresponding to the front end portions of the respective ink chambers 45, and these communicate with the respective ink chambers 45. In addition, an ink supply port 49 communicating with the nozzle plate 43 where the common ink chamber 46 is located is formed. The ink is supplied from the external ink tank 5 (see FIG. 1) to the common ink chamber 46 through the ink supply port 49. The ink supplied to the common ink chamber 46 is supplied to each independent ink chamber 45 through each ink supply path 47.
[0026]
Each of the independent ink chambers 45 has a thin bottom wall 51 and is set to function as a diaphragm that can be elastically displaced in an out-of-plane direction, that is, in a vertical direction in FIG. Therefore, the bottom wall 51 may be referred to as a diaphragm for the sake of convenience in the following description.
[0027]
Next, in the glass substrate 44 located under the silicon substrate 42, the surface of the glass substrate 44, which is the upper surface, which is to be bonded to the silicon substrate 42, is shallowly etched at a position corresponding to each ink chamber 45 of the silicon substrate 42. The formed concave portion 52 is formed. Therefore, the bottom wall 51 of each ink chamber 5 faces the glass substrate surface on which the concave portion 52 is formed with a very small gap G therebetween. The distance between the bottom wall 51 and the surface of the glass substrate will be described later in detail.
[0028]
The bottom wall 51 of each ink chamber 45 functions as a common electrode on each ink chamber side. A segment electrode 55 is formed on the surface of the concave portion of the glass substrate 44 so as to face the bottom wall 51 of each ink chamber. The surface of each segment electrode 55 is covered with an insulating layer 56 made of inorganic glass. As described above, with the insulating layer 56 formed on the segment electrode 55 and the gap G interposed therebetween, each ink chamber bottom wall 51 and the corresponding segment electrode 55 form a counter electrode. A common electrode terminal 57 is formed on the conductive silicon substrate 42, and a driving voltage pulse is applied between the common electrode terminal 57 and each segment electrode 55.
[0029]
In the inkjet head 1 having this configuration, when a driving voltage pulse is applied between the electrodes, a Coulomb force is generated by the electric charge charged between the opposing electrodes, and the bottom wall (diaphragm) 51 moves toward the segment electrode 55. The bending of the ink chamber 45 increases. Next, when the drive voltage between the electrodes is released and the electric charge between the electrodes is discharged, the diaphragm 51 is restored by its elastic restoring force, and the volume of the ink chamber 45 is rapidly contracted. Due to the ink pressure generated at this time, a part of the ink filling the ink chamber 45 is ejected as an ink droplet from the ink nozzle 48 communicating with the ink chamber. However, in this example, as described below, a portion of the vibration plate 51 that is hardly bent in an out-of-plane direction is formed so that ink droplets smaller than the ink nozzle diameter can be ejected.
[0030]
Referring to FIG. 2, the back surface of each vibration plate 51 is a flat surface, but the side of the glass substrate 44 is deepened stepwise toward the longitudinal direction of the ink chamber 45. The portion where the base end side of the ink chamber 45, that is, the portion of the vibration plate 51 on the side of the ink supply path 47 is opposed, is the smallest gap G1. A portion of the middle portion of the ink chamber 45 adjacent to the gap G1 and facing the portion of the vibration plate 51 is a medium gap G2 larger than this. The largest gap G3 is formed at the end of the ink chamber 45, that is, at the portion of the vibration plate 51 near the ink nozzle 48. Of course, these gaps are, as shown in FIG. 4, exactly the distance from the front surface of the insulating layer 56 to the back surface of the diaphragm 51.
[0031]
Since the gaps are different as described above, even if the same drive voltage pulse is applied, the portion of the diaphragm 51 that is elastically displaced and is suction-joined to the segment electrode 55 side differs depending on the magnitude thereof. The portion 51a of the diaphragm 51 corresponding to the widest gap G3 is a portion that is finally elastically displaced and sucked, and this is a portion of the diaphragm 51 that is difficult to bend in this example, and the other portions are relatively fixed. This is a portion that is easily bent.
[0032]
With reference to FIG. 5, the operation of the inkjet head 4 of this example will be described. The gap G between the vibration plate 51 and the segment electrode 55 is formed such that the smallest gap G1, the middle gap G2, and the largest gap G3 are located at their base ends in the longitudinal direction of the ink chamber 45. They are formed in this order from the side toward the tip.
[0033]
When a driving voltage pulse having a small waveform, that is, a driving voltage pulse P1 having a small pulse height and a small width as shown in FIG. 5C is applied (charged) between the electrodes, FIG. As shown in the figure, first, the portion 51c of the diaphragm corresponding to the smallest gap portion G1 is elastically displaced and sucked toward the segment electrode 55, and then the portion 51b corresponding to the gap portion G2 is elastically displaced. It is sucked. However, the portion 51a corresponding to the widest gap portion G3 is not elastically displaced and attracted to the segment electrode 55 side. Thereafter, when the application of the small waveform drive voltage pulse P1 stops, the diaphragm 51 elastically returns. Due to the vibration of the vibration plate 51, a small-mass ink droplet is ejected from the ink nozzle 48.
[0034]
On the other hand, when a driving voltage waveform having a large waveform, that is, a driving voltage pulse P2 having a large pulse height and a large width as shown in FIG. As shown in b), the hardly bent portion 51a of the diaphragm 51 is also attracted to the segment electrode 55 side, and the diaphragm 51 is entirely attracted to the segment electrode 55 side. Due to the overall elastic displacement of the vibration plate 51, a large amount of ink droplet is ejected from the ink nozzle 48.
[0035]
The illustrated electrostatic inkjet head 4 is of a face eject type in which ink droplets are ejected from ink nozzles provided on the upper surface of a semiconductor substrate. An edge eject type in which droplets are ejected from an ink nozzle provided at an end of the substrate may be used.
[0036]
(Drive control device)
Next, FIG. 6 is a schematic block diagram illustrating an example of a drive control device of the inkjet printer 1 of the present embodiment. The drive control device 61 of the present example has an inkjet head control unit 62 mainly configured by a CPU. Printing information is supplied to the CPU from an external device 63 via a bus, and a ROM, a RAM, and a character generator 64 are connected via an internal bus.
[0037]
The inkjet head control unit 62 executes a control program stored in the ROM using a storage area in the RAM as a work area, and executes a control signal for driving the inkjet head based on character information generated from the character generator 64. Generate The control signal becomes a drive control signal corresponding to the print information via the logic gate array 65 and the drive pulse generation circuit 66, and is supplied to the head driver IC 66 formed on the head substrate 68 via the connector 67. . Further, the drive voltage pulse signal V3, the control signal LP, and the polarity inversion control signal REV are also supplied to the head driver IC 66.
[0038]
In the head driver IC 66, a driving voltage pulse to be applied to each diaphragm 51 of the ink jet head 4, that is, a common electrode, is supplied to the common output terminal based on each of the supplied signals and the driving voltage Vp supplied from the power supply circuit 70. A drive voltage pulse output from the COM and applied to each counter electrode (individual electrode) corresponding to each ink nozzle 48 is output from the number of individual output terminals SEG corresponding to each individual electrode. The potential difference between the output of the common output terminal COM and the output of the individual output terminal SEG is applied between each of the vibration plates 51 corresponding to each of the ink nozzles and the individual electrodes facing each other. A driving potential difference waveform in a designated direction is applied during driving (when ink droplets are ejected), and no driving potential difference is applied when not driving.
[0039]
The drive pulse generation circuit 66 generates a drive voltage pulse having a predetermined pulse width and a control signal LP for forming one print pixel with the determined number of ejections, and outputs the control signal LP to the head driver IC 66.
[0040]
(Printing operation)
In the ink jet printer 1 of this example, it is possible to perform printing control in a plurality of printing modes. For example, one print pixel can be printed by 4 shot (shot) / dot (dot) drive, which is formed by ejecting ink droplets up to four times in a row. Also, by changing the number of ejections of ink droplets during one pixel printing period and the ejection mass of ink droplets at each ejection in two stages, the ink mass for forming each pixel is controlled, Can be performed. The print mode can be selectively switched by an input from the external device 3 side.
[0041]
FIG. 7 shows signal waveforms of various parts in the print mode by 4 shot / dot drive. In each figure, a drive voltage pulse signal V3, a control signal (latch pulse) LP, a polarity inversion control signal REV, a COM output which is an output of the common terminal COM, and a common voltage are supplied from the inkjet head control unit 62 to the head driver IC 66. 3 shows three examples of a COM-SEG potential difference, which is a potential difference (nozzle driving voltage waveform) generated between an electrode (diaphragm 51) and an individual electrode.
[0042]
In the print mode by the 4-shot / dot drive, eight gradation printing can be performed by a combination of the number of ejections of ink droplets and the mass of each ink droplet (exactly, the case where printing is not performed is included. And 9 gradations).
[0043]
FIG. 8 shows a list of the ink masses required for one-pixel printing at each gradation and the combinations of the number of ejections of the small mass ink droplet and the number of ejections of the large mass ink droplet to obtain each ink mass. It is shown in a table. As shown in this figure, in this example, a setting is made such that a driving voltage pulse P1 having a small waveform discharges 5 ng ink droplets, and a driving voltage pulse P2 having a large waveform discharges 15 ng ink droplets. .
[0044]
The gradation expression of the density is realized by increasing the ink mass for forming one-pixel printing every 5 ng. Accordingly, in the case of printing with the ink density of 5 ng, which is the lightest density, as shown by the waveform of the potential difference 1 in FIG. Let it. Further, in the case of one-pixel printing with an ink mass of 20 ng, as shown by the waveform of the potential difference 2 in FIG. 7, a small-mass ink droplet is ejected only once using a small-waveform drive voltage pulse P1. A large-mass ink droplet is ejected only once using the large-waveform drive voltage pulse P2. Further, in the case of one-pixel printing with the ink density of 40 ng of the maximum density, as shown by the waveform of the potential difference 3 in FIG. At the same time, a large-mass ink droplet is ejected twice using the large-waveform drive voltage pulse P2.
[0045]
As described above, in the present example, the first grayscale having the highest density performs four consecutive shots (two small-mass shots and two large-mass shots) in one pixel printing period T. The second gradation is three shots (one small-mass shot and two large-mass shots), the third gradation is two shots (two large-mass shots), The gradation is 3 shots (two small-mass shots and one large-mass shot), the fifth gradation is two shots (one small-mass shot and one large-mass shot), and the sixth gradation is 1 shot. The shot (one large-mass shot), the seventh gradation can be obtained by two shots (two small-mass shots), and the eighth gradation can be obtained by one shot (one small-mass shot).
[0046]
Here, in the case of performing density expression of eight gradations by ejecting ink droplets of the same mass as in the related art, it is necessary to eject ink droplets any number of times from once to eight times. However, the maximum number of ejections in the print mode of this example is only four. Therefore, multi-level density expression can be realized at a higher printing speed than before.
[0047]
Further, in this example, as the drive voltage pulse signal V3 for the 4-shot / dot mode, the drive voltage pulse P1 having a small waveform is continuously applied twice in one pixel printing period T, and then the drive voltage pulse P2 having a large waveform is obtained. Is used twice. When the ink droplet is ejected a plurality of times, the potential difference between the electrodes is formed so as to continuously eject the ink droplet. For example, when performing one-pixel printing with an ink mass of 20 ng, as shown in the waveform of the potential difference 2 in FIG. 7, the second small drive voltage pulse P1 (2) and the first large drive voltage pulse P1 (2) are used. The in-droplet is ejected at the time of ejection of the ink droplet by the drive voltage pulse P2 (1) having the waveform. Although not shown, when printing one pixel with an ink mass of 25 ng, the first large voltage pulse P1 (1), P1 (2), which is generated successively with the driving voltage pulses P1 (1) and P1 (2) having a continuous small waveform. Ink droplets are ejected at the time of ejection of ink droplets by the drive voltage pulse P2 (1) having a waveform.
[0048]
As described above, in the ink jet printer of this example, when printing of one pixel is formed by discharging ink droplets a plurality of times, a continuous ink droplet discharging operation is always performed. As a result, compared to the case where a plurality of times of ink ejection is performed in a discontinuous state within one pixel printing period and printing of one pixel is performed, the collection of the ejected ink droplets that land on the recording medium is improved, The print quality of a print image formed by multiple shots / dots can be stabilized.
[0049]
Further, in this example, the polarity of the potential difference applied for discharging the ink droplets is alternately inverted by the polarity inversion control signal REV. By inverting the polarity of the potential difference generated between the common electrode and the individual electrode in this way, a residual charge is generated between the electrodes, the electrostatic force fluctuates, and the desired ink ejection characteristics cannot be obtained. This can avoid the adverse effect of the situation. In particular, in this example, as in the case of the four-shot / dot mode described above, when printing one pixel by discharging a small amount of ink droplets a plurality of times, and discharging a large amount of ink droplets a plurality of times, When one pixel is printed, the number of ejections of ink droplets by each mass is set so that these ink droplets are ejected an even number of times. By setting the number to an even number, the same number of forward and reverse alternating energizations can always be realized. As a result, an increase in the residual charge between the electrodes can be suppressed, so that a proper ink droplet ejection operation is always guaranteed.
[0050]
(Another example of inkjet head)
In this example, as shown in FIG. 5, the portion 51a of the diaphragm 51 that is hardly bent is formed by partially widening the gap G between the diaphragm 51 and the segment electrode 55. The portion that is difficult to bend can be formed as shown in FIGS.
[0051]
The example shown in FIG. 9 is an example in which the width of each of the ink chambers 45 is changed to form a portion where the diaphragm is hardly bent. In this example, one side in the longitudinal direction of the diaphragm 51, which is the bottom wall of the ink chamber 45, is a wide portion 52b, and the other side is a narrow portion 52a. The narrow width portion 52a has higher out-of-plane rigidity than the wide width portion 52b, and thus is a portion that is difficult to bend. According to this configuration, the same operation and effect as those of the above example can be obtained.
[0052]
In the example shown in FIG. 10, a portion where the segment electrode 55 faces and a portion where the segment electrode 55 does not face are formed on the diaphragm 51. The portion of the diaphragm 51 that does not face the segment electrode 55 is a portion that is not easily bent.
[0053]
The example shown in FIG. 11 is an example in which a portion that is not easily bent is formed by changing the thickness of the diaphragm. In this example, one side in the longitudinal direction of the diaphragm 51 is made thinner, and the other side is made thicker. Since the portion 51d on the thicker side has high out-of-plane rigidity, this portion functions as a portion that is difficult to bend.
[0054]
Next, as an inkjet head capable of ejecting ink droplets having different masses, an inkjet head having a structure shown in FIG. 12 can be used. As shown in this figure, the basic configuration of the ink jet head 4A of this embodiment is the same as that of each of the above embodiments, except that the electrodes facing the diaphragm 51 are the segment electrodes 55A and the auxiliary electrodes 55B. The point is that the gap G between the auxiliary electrode 55B and the diaphragm 51 is narrowed by projecting the electrode glass substrate 44 side.
[0055]
That is, as shown in FIG. 12A, in the ink jet head 4A of this example, apart from the segment electrode 55A facing the diaphragm 51, an auxiliary electrode 55B facing the diaphragm 51 is formed separately. The configuration is such that charging and discharging can be performed independently of the portion of the diaphragm 51 facing 55. The auxiliary electrode 55B is opposed to each diaphragm 51, and each auxiliary electrode 55B is conductive as one electrode.
[0056]
In the ink jet head 4A having this configuration, as shown in FIG. 12B, a drive voltage pulse P1 having a small waveform (see FIG. 5C) is applied between the segment electrode 55A and the auxiliary electrode 55B and the diaphragm 51. When the voltage is applied, the portion of the vibration plate 51 corresponding to the auxiliary electrode 55B bends, thereby discharging a small-mass ink droplet. On the other hand, as shown in FIG. 12C, when a large waveform driving voltage pulse P2 (see FIG. 5D) is applied between the segment electrode 55A and the auxiliary electrode 55B and the diaphragm 51, The vibrating body 51 bends as a whole, thereby discharging a large amount of ink droplets.
[0057]
(Other embodiments)
In the above example, an ink jet head of an electrostatic drive type is used, but an ink jet head other than the electrostatic drive type, for example, an ink jet head of a type in which a discharge pressure of ink droplets is generated using a piezoelectric element or a heating element. The present invention is applicable to a head.
[0058]
【The invention's effect】
As described above, in the inkjet head driving method and the inkjet printer of the present invention, one-pixel printing is performed by ejecting ink droplets having different masses once or a plurality of times. Therefore, by appropriately combining the number of ejections and the ejection mass of the ink droplets, the number of ejections of the ink droplets can be reduced as compared with the case where the same mass of ink droplets are ejected a plurality of times to perform one-pixel printing of a predetermined density. Since it can be reduced, the printing speed can be increased. Further, compared with a case where one-pixel printing of a predetermined density is performed by ejecting ink droplets of the same mass a plurality of times, it is possible to express the density with finer gradation.
[0059]
Further, in the present invention, when one-pixel printing is performed by discharging ink droplets a plurality of times, ink droplets are discharged at a continuous timing within a one-pixel printing period. Therefore, compared with a case where a plurality of ink ejections are performed in a discontinuous state in one pixel printing period and printing for one pixel is performed, a group of the ejected ink droplets that land on the recording medium is improved. In addition, it is possible to stabilize print quality of a print image formed by multi-shot one-pixel printing.
[0060]
Further, when an electrostatic drive type ink jet head is used, the polarity of the voltage applied between the opposing electrodes is switched between forward and reverse alternately. The number of ejections is set to be an even number. As a result, a voltage is always applied between the electrodes alternately in the normal and reverse directions, so that a residual charge is generated between the electrodes, the electrostatic force fluctuates, and the desired ink ejection characteristics cannot be obtained. The disadvantage of doing so can be avoided.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an ink jet printer to which the present invention is applied.
FIG. 2 is a schematic sectional view illustrating a configuration example of an inkjet head of the inkjet printer of FIG.
FIG. 3 is a plan configuration diagram of the ink jet head of FIG. 2;
FIG. 4 is an enlarged partial cross-sectional view of the inkjet head of FIG. 2;
5 (a) and 5 (b) are diagrams showing the operation of the inkjet head of FIG. 2, and FIG. 5 (c) is a waveform diagram showing a small waveform driving voltage pulse applied between electrodes, and FIG. () Is a waveform diagram showing a drive voltage pulse having a substitute waveform applied between electrodes.
FIG. 6 is a schematic block diagram illustrating a drive control device in the inkjet printer of FIG. 1;
FIG. 7 is a timing chart showing signal waveforms at various portions in the 4-shot / dot drive in the inkjet printer of FIG. 1;
8 is an explanatory diagram showing a combination of the ejection mass of ink droplets and the number of ejections for expressing a density in 4-shot / dot driving in the inkjet printer of FIG. 1;
FIG. 9 is a plan view showing another example of the inkjet head of FIG. 2;
FIG. 10 is a sectional view showing another example of the ink jet head of FIG. 2;
FIG. 11 is a cross-sectional configuration diagram illustrating another example of the inkjet head of FIG. 2;
FIG. 12 is an explanatory diagram showing another example of the ink jet head of FIG. 2;
[Explanation of symbols]
1 Inkjet printer
4 Inkjet head
45 Ink chamber
46 Common ink chamber
48 ink nozzle
51 diaphragm
51a Vibration plate hardly bent
51b, 51c Flexible portion of diaphragm
52 recess
55 segment electrode
G, G1, G2, G3 Distance between electrodes
P1, P1 (1), P1 (2) Small waveform drive voltage pulse
P2, P2 (1), P2 (2) Large waveform drive voltage pulse
61 Inkjet head drive control device
62 Inkjet head controller
66 Drive pulse generation circuit
T 1 pixel printing period

Claims (12)

In a method for driving an ink-jet head for forming a print for one pixel by discharging ink droplets once or more times,
The mass of ink droplets ejected from the same ink nozzle is made variable,
A method for driving an ink-jet head, characterized in that printing of the one pixel is performed by discharging at least once an ink droplet having a predetermined mass from the ink nozzle. In claim 1,
The ejection mass of ink droplets ejected from the ink nozzle can be changed in at least two stages,
In order to obtain the ink mass required for printing for one pixel, the combination of the number of times of ink droplet ejection and the mass of each ink droplet ejected is set such that the number of times of ink droplet ejection by the ink nozzle is minimized. A method for driving an ink-jet head, characterized in that it is determined. In claim 2,
In the case where the printing of one pixel is formed by discharging ink droplets a plurality of times, the ink droplets are continuously discharged at a predetermined minimum drive cycle. Method. In claim 1,
The ink jet head includes a plurality of the ink nozzles, an ink pressure chamber communicating with each ink nozzle, a vibrating plate that vibrates in an out-of-plane direction forming a part of each ink pressure chamber, and a vibrating plate. An electrostatic drive type comprising an opposing electrode disposed oppositely, and applying a drive voltage pulse between the diaphragm and the opposing electrode to deform the diaphragm and eject ink droplets from the ink nozzles. A method for driving an ink-jet head, comprising: In claim 4,
A method for driving an ink jet head, wherein a driving voltage pulse having a different waveform is applied between the vibration plate and the counter electrode to change a discharge mass of ink droplets discharged from the ink nozzle. In claim 5,
The gap between the diaphragm and the counter electrode is changed in two or more stages,
By ejecting a small mass ink droplet from the ink nozzle by deformation of the portion of the diaphragm corresponding to the narrow gap portion,
A method for driving an ink-jet head, characterized in that a large mass of ink droplets is ejected from the ink nozzles by deformation of a portion of the vibration plate corresponding to a wide gap portion. In claim 5 or 6,
A portion that is easily bent and a portion that is not easily bent are formed on the diaphragm,
Discharging small ink droplets from the ink nozzles by deforming the flexible portion,
A method for driving an ink-jet head, characterized in that a large-mass ink droplet is ejected from the ink nozzle by deformation of the hardly bent portion. In any one of claims 5 to 7,
A combination of the number of times of ink droplet ejection and the mass of each ink droplet ejected is determined so that the ink mass required for printing for one pixel can be obtained with the minimum number of times of ink droplet ejection by the ink nozzle. A method for driving an ink-jet head, comprising: In claim 8,
In the case where the printing for one pixel is formed by discharging ink droplets a plurality of times, the ink droplets are continuously discharged at a predetermined minimum drive cycle. Method. In claim 9,
A method for driving an ink-jet head, characterized in that the drive voltage pulse is applied between the diaphragm and the counter electrode so that the direction of current application is alternately reversed. In claim 10,
In the case where the driving voltage pulse having a plurality of small waveforms and / or the driving voltage pulse having a large waveform is applied a plurality of times for printing the one pixel, the driving voltage pulse having an even number of small waveforms is applied. And / or applying the driving voltage pulse having a large waveform even number of times. An ink-jet printer which performs printing of one pixel by the method of driving an ink-jet head according to any one of claims 1 to 11.

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