JP2005246663A - Liquid ejection head and driving method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate unevenness in printing density so as to prevent deterioration in image quality, by preventing the occurrence of a standing wave so as to prevent lack of the replenishment quantity of ink and the downsizing of an ink droplet. <P>SOLUTION: When f represents a driving frequency for driving a heating resistor and Lfn represents the length of a common channel wherein the standing wave is generated in the ink, the actual length L of the common channel is set not to correspond to Lfn. When L represents the length of the common channel and Fn (a suffix n represents an nth-order harmonic index) represents the number of vibrations generated in the ink in common channel by the standing wave, the driving frequency f for actually driving the heating resistor is set not to correspond to Fn. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the liquid discharge head which discharges the liquid in the liquid chamber from the nozzle by driving the liquid discharge means, a standing wave is generated in the liquid in the common liquid flow path communicating with all the liquid chambers. In particular, the liquid discharge head and the liquid discharge head driving method are described. More specifically, the length of the liquid flow path is defined in relation to the drive frequency of the liquid discharge means to generate a standing wave. The present invention relates to a method of driving a liquid discharge head that prevents the occurrence of standing waves by defining the drive frequency of the liquid discharge means in relation to the prevented liquid discharge head and the length of the liquid flow path.

In a printer head of an ink jet printer, which is one of liquid ejection heads, a conventional ink channel structure is known in which an ink channel is formed by a channel plate so as to communicate with an ink pressurizing chamber. (For example, refer to Patent Document 1).
JP 2003-136737 A

  In the technique disclosed in Patent Literature 1, the inlet portion of the ink pressurizing chamber forms an individual flow path for each ink pressurizing chamber. Further, the ink flow path forms a common flow path for supplying ink to the individual flow paths of all the ink pressurizing chambers.

  In each nozzle of the printer head, generally, a heating element (a heating resistor or the like) is heated to generate bubbles, and ink is ejected by pressure due to the expansion, or an electric signal is applied to the piezo element, Ink is ejected by the pressure accompanying the dynamic motion.

FIG. 7 is a diagram schematically showing a printer head provided with the ink liquid chamber 12 (corresponding to the ink pressurizing chamber of the above-mentioned Patent Document 1), and is a diagram for explaining operations at the time of ink ejection in time series. .
FIG. 8 is a graph showing the relationship between bubble pressure and bubble volume in the time series of FIG.

  In order to eject ink by the heating resistor 13 shown in FIG. 7, the heating resistor 13 is heated for 1 to several microseconds. Then, the ink is heated rapidly, and the ink temperature rises beyond the boiling point (see ~ t0 in FIG. 7). When the ink temperature reaches the spontaneous nucleation temperature (300 ° C.), numerous bubble nuclei are instantaneously generated on the heating surface (see t0 in FIGS. 7 and 8), and excess energy in the ink is released at once. Then, it boils explosively and the bubble pressure rises (see t0 to t1 in FIGS. 7 and 8). The bubble pressure reaches a maximum of several tens of atmospheres in an instant, and adiabatic expansion and expansion receiving heat from the surroundings occur simultaneously, and bubbles rapidly grow (see t1 to t2 in FIGS. 7 and 8).

  Thereafter, the bubble pressure falls below atmospheric pressure and the expansion rate slows, but the bubble volume reaches a maximum. Therefore, the ink is accelerated up to about 10 m / s by the expansion moment of the bubbles and jumps out of the nozzle, and the bubbles are depressurized along with the expansion (see t3 in FIGS. 7 and 8). Then, due to the inertia of the ink and the vapor condensing (condensation) and the bubbles contract, the tail of the expanded ink is cut and ejected from the nozzle 18 as ink droplets (t3 in FIG. 7 and FIG. 8). t4). The bubbles collapse and disappear on the heating surface (see t4 in FIGS. 7 and 8), and this time, the ink is replenished with the capillary force of the ink liquid chamber 12 as the driving force (t4 in FIG. 7). ~reference).

By the way, in the printer head, a serial head that performs printing by moving the head in the width direction of the recording medium and a number of heads arranged in the width direction of the recording medium are formed to form a head corresponding to the printing width. Thus, there is a line head for forming an image in a band shape (not a line shape).
The line head can form an image without moving the head (without performing sub-scanning) by setting the length of the head to be equal to or larger than the width of the target printed matter. That is, since there are many nozzles and there is no need for sub-scanning, printing can be performed at high speed.

FIG. 9 is a perspective view showing a part of such a line head 10.
As shown in FIG. 9, the line head 10 forms a head chip 19 in which the heating resistors 13 are arranged in one direction, a nozzle sheet 17 on which nozzles 18 are formed, and an ink liquid chamber 12 corresponding to the nozzles 18. And a barrier layer 15 for the purpose. The common flow path member 20 forms a common ink flow path 21 (corresponding to the ink flow path of Patent Document 1) that communicates with all the ink liquid chambers 12. For example, for the A4 printer, the length of the line head 10 is 220 mm, which corresponds to at least the short side of the A4 size.

  Here, in the technique of the above-mentioned Patent Document 1, as shown in FIG. 9, when the bubble is expanded by heating the heating resistor 13, the bubble pressure is increased from the inside of the ink liquid chamber 12 to the ink common channel 21 side. There is a problem that pressure waves are propagated. That is, since the bubbles grow evenly, the bubble pressure has the effect of pushing the ink back toward the common flow path 21 (arrow pointing downward to the right), in addition to pushing the ink in the direction of the nozzle 18 and discharging it (arrow pointing downward). There is also. Therefore, a pressure wave is propagated to the common flow path 21 side.

  This will be described in detail. As shown in FIG. 9, the ink in the ink liquid chamber 12 is instantaneously compressed toward the common flow path 21 by the bubbles generated by heating the heating resistor 13 (right side). (Down arrow), released immediately after. In this way, the compression toward the common flow path 21 side then instantaneously compresses and releases the ink slightly ahead. Then, by compressing and releasing the adjacent portions of the ink portions one after another, the pressure wave travels toward the common flow path 21. Here, during printing, the nozzle 18 continuously ejects ink. Therefore, a continuous pressure wave is generated, and in the ink in the common flow path 21, a pressure density wave (longitudinal wave) is formed along the pressure wave traveling direction (parallel to the traveling direction). The

FIG. 10 is a plan view showing pressure wave propagation in the line head 10.
As shown in FIG. 10, the pressure wave generated from the central heating resistor 13 propagates along the common flow path 21. The shape of the common channel 21 is generally tubular and has a long tube length with respect to the cross-sectional area. Since the attenuation rate is small because there is no diffusion inside the common channel 21, the pressure wave eventually reaches the end of the common channel 21 and is reflected. The reflected pressure wave travels in the opposite direction and is eventually reflected at the opposite end. This is repeated until the pressure wave decays.

  By the way, the line head 10 has many nozzles 18 as shown in FIG. 9, and these individually eject ink. Therefore, many pressure waves are sent into the common flow path 21 from many nozzles 18 at various timings. Then, as a result, the frequency component of the composite wave in the common flow path 21 is wide from low frequency to high frequency. And the frequency component which satisfy | fills a certain condition among these generates a standing wave in the common flow path 21.

Since the pressure wave propagating in the liquid called ink in the common flow path 21 is reflected with both ends of the common flow path 21 as fixed ends, the length of the common flow path 21 is L and the wavelength of the pressure wave is λ. The condition for generating a standing wave is
L = n · λ / 2 (where n is a natural number)
It is.

Also, between the sound velocity v in the ink, the pressure wave wavelength λ, and the pressure wave frequency f,
v = fλ
There is a relationship.
Therefore, the condition for generating a standing wave is
L = n · v / (2f) (where n is a natural number)
It can also be expressed as The frequency f is not limited to the frequency at which ink is ejected and its harmonics, but is a frequency component of the combined wave of pressure waves emitted from many nozzles 18.

  In the condition where the standing wave is generated, when n = 1, both ends of the common flow path 21 are nodes and the center is an antinode. In the case of n = 2, both ends and the center of the common flow channel 21 are nodes, and 1/4 and 3/4 portions are antinodes. That is, the ink cannot vibrate at the end of the common channel 21 because it is blocked by a hard wall surface. In addition, at the portion of the node other than the end portion of the common flow path 21, the vibration of the ink is canceled and the stationary portion is stationary. Conversely, the ink vibrates in the belly portion.

  Therefore, the velocity of vibration of the particles in the ink (acoustic particle velocity) is large in the antinode portion and small in the node portion. For this reason, in the antinode portion where the particle speed is high, the distance between the particles is increased and the density is reduced. In other words, since the density is low, it can be said that it can vibrate violently. On the other hand, in the portion of the node where the particle velocity is low, the particles are close to each other, so the density is high. The pressure is low when the density is low, and the pressure is high at the portion where the density is high.

  The pressure difference in the common flow path 21 affects the ink supply efficiency to each ink liquid chamber 12. That is, the high pressure promotes the ink supply to the ink liquid chamber 12, so that the ink supply efficiency is high, and the low pressure acts in the direction of hindering the ink supply, so the ink supply efficiency is low. Therefore, in the ink liquid chamber 12 in the low pressure portion of the common flow path 21, it takes time to replenish the ink after the ink is ejected from the nozzle 18. In particular, the supply of ink to the fine nozzle 18 having a diameter of several μm to several tens of μm and the maintenance of the meniscus (ink liquid level at the nozzle 18) after the ink supply are performed by the capillary force of the nozzle 18 and the ink liquid chamber 12. Since it is based on a delicate balance with the internal pressure, the influence of the internal pressure change in the common flow path 21 is large.

  When the pressure difference in the common flow path 21 becomes larger than a certain level, a situation in which replenishment of ink does not complete before the next ink discharge is started in the low pressure portion (the antinode portion of the standing wave). . Then, the ink replenishment amount is insufficient, the size of the ink droplet ejected from the nozzle 18 is reduced, the dots formed by the landing of the ink droplet are also reduced, and the printing density is reduced. In particular, in the case of the line head 10, since the head is not scanned, the density difference between individual dots is expressed as a streak on the photographic paper. As a result, the density is printed lightly in the belly portion.

FIG. 11 is a diagram showing the relationship between the standing wave generated in the common flow path 21 and the print density, and summarizes the relationship between the standing wave and the print density described above.
As shown in FIG. 11, the pressure in the common flow path 21 is low at the belly portion where the ink particle velocity is high. As a result, the ink supply efficiency is lowered and the ink replenishment time is increased. As a result, the ink replenishment amount is insufficient, the ink droplet size is reduced, and the print density is reduced. In addition, at the node portion where the ink particle velocity is low, the pressure in the common flow path 21 is high, so that the ink supply efficiency is increased, and the ink replenishment time is shortened. The droplet size increases and the print density increases.

  In this way, under certain conditions, a standing wave due to an ink density wave is generated in the printer head due to a pressure wave accompanying the ejection of ink droplets. This standing wave becomes unevenness of the printing density and is expressed in a streak pattern on the printing paper, causing deterioration of the image quality. And the above-mentioned patent document 1 does not disclose prevention of such image quality deterioration.

  Therefore, the problem to be solved by the present invention is to prevent the standing wave from being generated, to prevent the ink replenishment amount from being insufficient and the ink droplet size from being reduced, thereby reducing the print density. It is an object to provide a liquid discharge head that can eliminate unevenness and prevent deterioration of image quality and a method for driving the liquid discharge head.

The present invention solves the above-described problems by the following means.
According to a first aspect of the present invention, there is provided a head chip in which a plurality of energy generating elements are arranged in one direction, a nozzle sheet in which nozzles for discharging droplets are formed, and the head chip. A liquid chamber forming member that is stacked between the formation surface of the energy generating element and the nozzle sheet and that forms a liquid chamber corresponding to each nozzle, and communicates with all the liquid chambers of the head chip. A common flow path member for forming a common flow path for the liquid, and driving the energy generating element to discharge the liquid in the liquid chamber as droplets from the nozzle and land on the recording medium for printing. The length of the common flow path in which the standing wave is generated in the liquid in the common flow path with respect to the drive frequency f (kHz) for driving the energy generating element is Lfn (mm ) Can, the length of the common flow path L (mm), characterized in that so that they do not match the Lfn (mm).

  In the above invention, when the drive frequency f for driving the energy generating element is determined, the print flow density L is set so that the length L of the common flow path does not coincide with the length Lfn at which the standing wave is generated. This eliminates unevenness. In particular, when the standing wave generation length due to the fundamental vibration at the driving frequency f is Lf1, it is impossible in principle to generate a standing wave by making the length L of the common flow path shorter than Lf1. A liquid discharge head can be obtained.

  The invention according to claim 5, which is another one of the present invention, includes a head chip in which a plurality of energy generating elements are arranged in one direction, a nozzle sheet on which nozzles for discharging droplets are formed, A liquid chamber forming member for forming a liquid chamber corresponding to each nozzle, which is laminated between the formation surface of the energy generating element of the head chip and the nozzle sheet; and all the liquids of the head chip A common flow path member for forming a common flow path for the liquid communicating with the chamber, and driving the energy generating element to discharge the liquid in the liquid chamber as droplets from the nozzle, to the recording medium A method of driving a liquid discharge head that lands and prints, wherein a frequency at which a standing wave is generated in the liquid in the common flow path is set to Fn (L) with respect to the length L (mm) of the common flow path. kHz) (however, the subscript n is When the next harmonic index), the drive frequency f for driving the energy generating element (kHz), characterized in that to not coincide with the Fn (kHz).

  In the above invention, when the length L of the common flow path is determined, the print density is controlled by preventing the drive frequency f for driving the energy generating element from coincident with the frequency Fn at which a standing wave is generated. This eliminates unevenness. The subscript n of the frequency Fn means the nth-order harmonic exponent, and n = 1 is the fundamental vibration.

According to the liquid ejection head of the present invention, the length of the common flow path of the liquid communicating with all the liquid chambers does not match the length at which standing waves are generated in the liquid in the common flow path. A standing wave does not occur in the image, and unevenness in the print density is eliminated, thereby preventing image quality deterioration.
Further, according to the driving method of the liquid discharge head of the present invention, the drive frequency of the energy generating element that discharges the liquid from the nozzle does not coincide with the frequency at which a standing wave is generated in the liquid in the common flow path. Since the energy generating element is driven, no standing wave is generated in the liquid, the unevenness of the print density is eliminated, and the deterioration of the image quality is prevented.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the following embodiment, the liquid discharge head in the present invention corresponds to the line head 10 in an A4 size (paper width 210 mm) line-type inkjet printer. In the following embodiment, the liquid to be discharged is ink, and the liquid chamber for storing the ink is the ink liquid chamber 12, and a very small amount (for example, several picoliters) discharged from the nozzle 18 formed on the nozzle sheet 17 is used. The ink is an ink droplet.

  In the following embodiment, the heating resistor 13 is used as an energy generating element, and the heating resistor 13 also constitutes one surface (bottom wall portion) of the ink liquid chamber 12. Furthermore, in the following embodiment, the liquid chamber forming member corresponds to the barrier layer 15 constituting the side wall of the ink liquid chamber 12. The ink liquid chambers 12, the heating resistors 13, and the nozzles 18 are equivalent to the number corresponding to the A4 size print width, and all the ink liquid chambers 12 are formed by the common flow path 21 of ink formed by the common flow path member 20. Communicate.

FIG. 1 is a cross-sectional view showing a line head 10 of this embodiment.
As shown in FIG. 1, the line head 10 includes a nozzle sheet 17 in which a plurality of nozzles 18 are formed at equal intervals, and a head chip 19 in which a plurality of heating resistors 13 are arranged in one direction. They are bonded together via a barrier layer 15 constituting the chamber 12. Here, each nozzle 18 corresponds to each ink liquid chamber 12 and each heating resistor 13.

  Further, a common flow path member 20 is disposed above the head chip 19, and a common flow path 21 of ink formed by the common flow path member 20 communicates with all the ink liquid chambers 12. The central portion of the common flow path member 20 is connected to the ink tank 41 via the valve device 22, and the ink in the ink tank 41 is supplied from the common flow path 21 to each ink liquid chamber 12.

FIG. 2 is a block diagram for driving the heating resistor 13 of the line head 10.
As shown in FIG. 2, an ink ejection drive pulse control circuit generates ejection drive pulses under the control of the CPU in accordance with input data. Then, the head driving circuit heats the heating resistor 13 by this ejection driving pulse.

  As described above, at the time of printing, the heating resistor 13 shown in FIG. 1 generates heat by the ejection drive pulse corresponding to the input data, and the ink in the ink liquid chamber 12 is locally heated. Then, bubbles are generated in the ink liquid chamber 12 by this heating, and ink droplets are ejected from the nozzles 18 by the pressure of the bubbles, and the ejected ink droplets land on the photographic paper that is the recording medium, and character Images are printed. The ink droplets are ejected while feeding the photographic paper.

  Here, the ejection drive pulse generated by the drive pulse control circuit is a rectangular pulse having a predetermined width. When ink droplets are ejected continuously, this ejection drive pulse is made to continue at a constant period (ejection drive pulse period), which becomes the drive frequency of the heating resistor 13. Therefore, the ink needs to be replenished into the ink liquid chamber 12 during this ejection drive pulse cycle.

  By the way, a standing wave may be generated in the ink in the common flow path 21 of the line head 10 due to the pressure wave accompanying the ejection of the ink droplet. That is, it is considered that the standing wave is generated by the pressure wave generated when the ink droplet is ejected as a vibration source. Further, it is conceivable that the vibration when the photographic paper is fed is transmitted to the line head 10 and happens to coincide with the generated frequency of the standing wave.

  Since this standing wave causes unevenness in the print density, it is important to know the frequency at which the standing wave is generated, regardless of the cause. The generated frequency of the standing wave can be confirmed by a printing test. Therefore, a test method for confirming the frequency of standing waves by actually printing with the line head 10 will be described below.

FIG. 3 is a diagram showing the result of a printing test using the line head 10. For example, solid printing is performed when the line head 10 shown in FIG. 1 performs solid printing and the driving frequency of the heating resistor 13 is increased. It is a figure which shows (light / dark).
As shown in FIG. 3, when the drive frequency is gradually increased from fa to fg, the print density unevenness (light / dark) appears at a certain drive frequency fb higher than the initial drive frequency fa. In this case, it can be estimated that the uneven portion is the antinode position of the standing wave, and the shape of the standing wave estimated at the drive frequency fb is the fundamental vibration.

  When the drive frequency is further increased, unevenness (shading) is confirmed again at the drive frequency fd, and it can be estimated that a standing wave is also generated there. Further, the harmonic index n can be estimated by counting the number of the unevenness (shading). Note that the shape of the standing wave estimated at the drive frequency fd is double vibration, and similarly, the shape of the standing wave estimated at the drive frequency ff is triple vibration.

  Thus, by performing the printing test, it is possible to determine the frequency Fn of a standing wave that may be generated. Therefore, when the line head 10 shown in FIG. 1 is driven, a line in which no standing wave is generated in the ink in the common flow path 21 is obtained by making the driving frequency f not coincide with the frequency Fn of the standing wave. The head 10 can be obtained.

  Here, if the drive frequency f is slightly different from the frequency Fn of the standing wave, the wave travels and cannot be physically called a standing wave. However, if there is only a slight difference between the two, depending on the printed image, there is a possibility that unevenness in the print density remains to the extent that it can be visually confirmed. Therefore, a visual test using a monitor was conducted to such an extent that unevenness in the print density could not be visually confirmed. As a result, it has been found that if printing is performed at a driving frequency f that is 5% or more away from the frequency Fn of the standing wave, unevenness of the print density (shading) can be reduced to a level that is substantially free of problems.

Therefore, if the frequency Fn of the standing wave is known, the drive frequency f of the heating resistor 13 shown in FIG.
(Fn) × 1.05 ≦ f ≦ (Fn + 1) × 0.95 (1) and by driving the heating resistor 13 within the range of the equation (1), The line head 10 can be configured such that no standing wave is generated in the ink. Note that the subscript n is an nth-order harmonic exponent.

In addition, it is obvious that the larger the drive frequency f is from the frequency Fn of the standing wave, the better. Therefore, it is particularly preferable to set the driving frequency f to an intermediate value between the standing wave frequencies Fn and Fn + 1. That is,
f = ((Fn) + (Fn + 1)) / 2... (2)

FIG. 4 is a diagram showing the relationship between the frequency Fn of the standing wave and the drive frequency f.
As described above, the drive frequency f farthest from the standing wave frequency Fn is an intermediate value between the standing wave frequencies Fn and Fn + 1. However, it is necessary to consider the error of the frequency Fn and the frequency Fn + 1 of the standing wave. Therefore, as shown in FIG. 4, the above equation (2) is given a range,
f = ((Fn) + (Fn + 1)) / 2 ± ((Fn) − (Fn + 1)) × 0.1
As a result, by driving the heating resistor 13 within this range, it is possible to obtain a safe driving frequency f with no unevenness (darkness) in print density.

Next, the relationship between the shape of the common channel 21 (see FIG. 1) and the frequency Fn of the standing wave will be described.
If the shape of the common channel 21 is complicated, it is difficult to obtain the standing wave frequency Fn by calculation. Therefore, the standing wave frequency Fn is confirmed by performing the printing test as described above. There is a need.

However, if the common flow path 21 (see FIG. 1) has a linear shape with both ends closed and a uniform cross-sectional shape, the frequency Fn of the standing wave can be obtained by calculation. That is, if the length of the common channel 21 is L (mm) and the sound velocity in the ink in the common channel 21 is v (m / s), the frequency Fn (kHz) at which a standing wave is generated is ,
(Fn) = n · v / (2L) (where n is a harmonic index).

FIG. 5 is a graph showing the relationship between the standing wave frequency Fn and the tube length Ln.
Since the line head 10 of the present embodiment corresponds to the A4 size (paper width 210 mm), if the length L of the common flow path 21 is 220 mm and the sound velocity of ink is 1450 m / s, the above ( From the equation (3), the relationship between the frequency Fn (kHz) of a standing wave having an nth-order harmonic index and the tube length Ln (mm) is as shown in the graph of FIG. Here, since L = 220 mm, the frequency Fn of Ln = 220 mm is a driving frequency to be avoided.

Moreover, said (1) Formula can be deform | transformed as follows. That is,
(N · v / (2L)) × 1.05 ≦ f ≦ ((n + 1) · v / (2L)) × 0.95 (4) The drive frequency f (kHz) within this range By driving the heating resistor 13, it is possible to prevent a standing wave from being generated in the ink in the common flow path 21 of the line head 10.

  Then, the relationship between the frequency Fn of the standing wave and the driving frequency f is obtained from the graph shown in FIG. 5 and the above equations (2) to (4). That is, from the graph shown in FIG. 5, the frequency Fn of the standing wave when the length L of the common flow path 21 is 220 mm is obtained, and the usable drive deviated by ± 5% from the above equation (4). The frequency f is obtained, and the most deviated ideal drive frequency f is obtained by the above equations (2) and (3).

FIG. 6 is a table showing the relationship between the frequency Fn of such a standing wave and the drive frequency f.
The relationship among the harmonic index n, the standing wave frequency Fn, the usable drive frequency f, and the ideal drive frequency f is as shown in FIG. 6, and the normal drive frequency is within the range of 5 to 20 kHz. In this case, with the line head 10 shown in FIG. 1, it is ideal to drive the heating resistor 13 at 5.6 kHz, 8.2 kHz, 11.5 kHz, 14.7 kHz, or 18.0 kHz. .

  In view of the printing speed, it is preferable that the drive frequency f be as high as possible. However, considering the ink replenishment time for the ink chamber 12 (see FIG. 1), the upper limit value of the drive frequency f is determined. Therefore, by setting the length of the common flow path 21 (see FIG. 1) that does not generate a standing wave for a certain driving frequency f (preferably an upper limit value), it is possible to prevent occurrence of uneven printing density. . That is, if the length of the common flow path in which the standing wave is generated in the ink in the common flow path 21 with respect to the driving frequency f is Lfn, the length L of the common flow path 21 is not matched with Lfn. To.

  Then, similarly to the determination of the driving frequency f described above, a visual test using a monitor was performed to such an extent that the unevenness in the print density could not be visually confirmed. As a result, 5% or more from the common flow path length Lfn where a standing wave is generated. It has been found that if the length is out of the range, the unevenness of the print density can be reduced to a level where there is substantially no problem.

Therefore, the length L of the common channel 21 is
By setting L ≦ 0.95 × Lfn or L ≧ 1.05 × Lfn (5), the line head 10 in which standing waves are not generated in the ink in the common flow path 21 can be obtained. In particular, if the length of the common flow path 21 where a standing wave is generated in the fundamental vibration of n = 1 is Lf1, the length L of the common flow path 21 is shorter than Lf1, for example,
L ≦ 0.95 × Lf1
By doing so, the generation of standing waves can be completely prevented.

As in the case of the drive frequency f described above, if the common channel 21 is a straight line with both ends closed and the cross-sectional shape is uniform, a common channel in which standing waves are generated by calculation. The length Lfn (mm) can be obtained. That is, if the drive frequency is f (kHz) and the sound velocity in the ink in the common flow path 21 is v (m / s), the length Lfn (mm) of the common flow path where the standing wave is generated is
Lfn = n · v / (2f) (where n is a natural number)
Can be calculated.

Therefore, the above equation (5) can be modified as follows. That is,
L ≦ 0.95 × n · v / (2f) or L ≧ 1.05 × n · v / (2f)
It becomes. By setting the length L (mm) of the common flow path 21 within this range, the line head 10 in which standing waves are not generated in the ink in the common flow path 21 can be obtained.

Thus, if the length L of the common flow path 21 is first determined or the driving frequency f of the heating resistor 13 is determined, the driving frequency to be avoided so as not to generate a standing wave, The length of the common flow path 21 to be avoided is known.
Therefore, by using the line head 10 having the common flow path 21 having the avoided length L or by driving the heating resistor 13 of the line head 10 at the avoided drive frequency f, the image quality is deteriorated due to the occurrence of standing waves. Can be prevented.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications such as the following are possible. That is,
(1) In this embodiment, a line head in which a large number of heads are arranged in the width direction of the recording medium is used. However, the present invention can also be applied to a serial head that performs printing by moving the heads in the width direction of the recording medium. is there.

  (2) In this embodiment, a thermal method using a heating resistor as an energy generating element is used. However, instead of a heating element such as a heating resistor, a diaphragm and an air layer are provided below the diaphragm. After applying the voltage between the two electrodes and bending the diaphragm, the electrostatic force is released and the diaphragm is returned to its original position. The present invention can also be applied to an electrostatic discharge method that discharges water. Further, the present invention can also be applied to a piezo method in which a laminated body of piezoelectric elements having electrodes on both surfaces and a diaphragm is used, and the diaphragm is deformed by the piezoelectric effect to eject ink droplets.

The liquid discharge head and the liquid discharge head driving method of the present invention are particularly suitable when applied to a printer head of an ink jet printer. However, the recording medium is not limited to photographic paper, for example, a liquid is applied to a film. The present invention can be applied to a medical liquid ejecting apparatus for ejecting, or a liquid ejecting apparatus for ejecting a dye to a dyed product.
Further, the present invention can be applied to a liquid ejection device that ejects a DNA-containing solution for detecting a biological sample.

It is sectional drawing which shows the line head of embodiment. It is a block diagram which drives the heating resistor of a line head. It is a figure which shows the result of the printing test by a line head. It is a figure which shows the relationship between the frequency Fn of a standing wave, and the drive frequency f. It is a graph which shows the relationship between the frequency Fn of a standing wave, and tube length Ln. It is a table | surface which shows the relationship between the frequency Fn of a standing wave, and the drive frequency f. It is a figure which shows typically a printer head provided with an ink liquid chamber. It is a graph which shows the relationship between bubble pressure and bubble volume. It is a perspective view which shows a part of line head. It is a top view which shows propagation of the pressure wave in a line head. It is a figure which shows the relationship between the standing wave which generate | occur | produced in the common flow path, and printing density.

Explanation of symbols

10 Line head 12 Ink liquid chamber (liquid chamber)
13 Heating resistor (energy generating element)
15 Barrier layer (liquid chamber forming member)
17 Nozzle sheet 18 Nozzle 19 Head chip 20 Common flow path member 21 Common flow path

Claims (8)

A head chip in which a plurality of energy generating elements are arranged in one direction;
A nozzle sheet on which nozzles for discharging droplets are formed;
A liquid chamber forming member that is stacked between the formation surface of the energy generating element of the head chip and the nozzle sheet, and forms a liquid chamber corresponding to each nozzle;
A common flow path member for forming a common flow path for liquid communicating with all the liquid chambers of the head chip,
A liquid discharge head that drives the energy generating element to discharge the liquid in the liquid chamber as droplets from the nozzle and land on a recording medium;
When the length of the common flow path in which the standing wave is generated in the liquid in the common flow path is Lfn (mm) with respect to the drive frequency f (kHz) for driving the energy generating element, the common flow A liquid discharge head characterized in that the path length L (mm) does not coincide with Lfn (mm). The liquid discharge head according to claim 1,
When the length of the common flow path in which the standing wave is generated in the liquid in the common flow path is Lfn (mm) with respect to the drive frequency f (kHz) for driving the energy generating element, the common flow The length L (mm) of the road is
L ≦ 0.95 × Lfn or L ≧ 1.05 × Lfn
A liquid discharge head characterized by that. The liquid discharge head according to claim 1,
When the length of the common flow path in which the standing wave due to the fundamental vibration is generated in the liquid in the common flow path is Lf1 (mm) with respect to the drive frequency f (kHz) for driving the energy generating element. , The length L (mm) of the common flow path,
L ≦ 0.95 × Lf1
A liquid discharge head characterized by that. The liquid discharge head according to claim 1,
The common flow channel is a straight channel having both ends closed and a uniform cross-sectional shape,
When the driving frequency for driving the energy generating element is f (kHz) and the sound velocity in the liquid in the common channel is v (m / s), a standing wave is generated in the liquid in the common channel. The length Lfn (mm) of the generated common flow path is
Lfn = n · v / (2f) (where n is a natural number)
As sought
The length L (mm) of the common flow path is
L ≦ 0.95 × n · v / (2f) or L ≧ 1.05 × n · v / (2f)
A liquid discharge head characterized by that. A head chip in which a plurality of energy generating elements are arranged in one direction;
A nozzle sheet on which nozzles for discharging droplets are formed;
A liquid chamber forming member that is stacked between the formation surface of the energy generating element of the head chip and the nozzle sheet, and forms a liquid chamber corresponding to each nozzle;
A common flow path member for forming a common flow path for liquid communicating with all the liquid chambers of the head chip,
A driving method of a liquid discharge head that drives the energy generating element to discharge the liquid in the liquid chamber as droplets from the nozzle and land on a recording medium,
The frequency at which a standing wave is generated in the liquid in the common flow path is Fn (kHz) with respect to the length L (mm) of the common flow path. ), The driving frequency f (kHz) for driving the energy generating element is not matched with Fn (kHz). The method of driving a liquid ejection head according to claim 5,
The frequency at which a standing wave is generated in the liquid in the common flow path is Fn (kHz) with respect to the length L (mm) of the common flow path. ), The drive frequency f (kHz) for driving the energy generating element is
(Fn) × 1.05 ≦ f ≦ (Fn + 1) × 0.95
A method of driving a liquid discharge head, characterized in that The method of driving a liquid ejection head according to claim 5,
The frequency at which a standing wave is generated in the liquid in the common flow path is Fn (kHz) with respect to the length L (mm) of the common flow path. ), The drive frequency f (kHz) for driving the energy generating element is
f = ((Fn) + (Fn + 1)) / 2 ± ((Fn) − (Fn + 1)) × 0.1
A method of driving a liquid discharge head, characterized in that The method of driving a liquid ejection head according to claim 5,
The common flow channel is a straight channel having both ends closed and a uniform cross-sectional shape,
When the length of the common channel is L (mm) and the speed of sound in the liquid in the common channel is v (m / s), a standing wave is generated in the liquid in the common channel. The frequency is Fn (kHz),
(Fn) = n · v / (2L) (where n is a harmonic index)
As sought
A drive frequency f (kHz) for driving the energy generating element is
(N · v / (2L)) × 1.05 ≦ f ≦ ((n + 1) · v / (2L)) × 0.95
A method of driving a liquid discharge head, characterized in that