JP2007062326A - Driving method of ink jet type recording head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving method which enables the record of a dot gradation in a stably high drive frequency region in the driving method which enables the control of the quantum of an ink drop by a multi-pulse drive. <P>SOLUTION: When the droplet is delivered using at least two or more consecutive electric pulses, each electric pulse is made into the same waveform shape. When time for meniscus of the above-mentioned nozzle orifice hole drawn at expansion process of the above-mentioned pressure chamber to reach the lowest point nearly is set to Tm, the time Tp from the time of starting the expansion process of the above-mentioned electric pulse to just before the start of the contraction process of the electric pulse is made almost equal to the Tm, and the total period of less than the natural period Tcxn (n is natural number) decided in the full width PW of the above-mentioned electric pulse in the ink passage from the above-mentioned nozzle orifice hole to the above-mentioned pressure chamber and the consecutive electric pulse keeps the above-mentioned electric pulse ranging over near the above-mentioned natural period Tcxn mostly. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a special liquid such as a recording head used in an image recording apparatus such as a printer, a color material liquid used for manufacturing a color filter of a liquid crystal display, or an electrode material liquid used for forming an electrode film such as an organic EL display. The present invention relates to a method for driving an ink jet head to be ejected.

  Various on-demand ink jet heads have been developed that form ink flow paths to nozzle opening holes, such as a common ink supply section and pressure chamber, and eject droplets by pressure generating means for expanding and contracting the pressure chamber. .

  Further, recent ink jet recording apparatuses can output high-definition images comparable to photographic image quality. This is because the ink flow path is miniaturized so that an extremely small droplet of several picoliters is ejected from a nozzle and selectively ejected onto a recording medium to output an image.

  On the other hand, there are printing apparatuses that print on very large recording media such as outdoor signboards and posters. These print qualities do not require so high definition and are printed by forming large dots with relatively large droplets. In order to obtain a large droplet, the large ink flow path is enlarged to eject the droplet. It has been very difficult to develop a head that makes these small droplets and large droplets compatible with one droplet.

  In order to realize such small droplets and droplets several times larger in size with one head, various ideas have been proposed in which an electric pulse for driving the pressure generating means is devised. For example, there has been proposed a method in which a plurality of ink droplets forming one dot are continuously ejected from a nozzle opening hole without being interrupted, united into one liquid during flight, and landed on a recording medium. In other words, by applying a plurality of continuous electric pulses to the pressure generating means and narrowing the slope or time interval of the subsequent electric pulses relative to the previous electric pulses, it can be obtained by the previous electric pulses in those electric pulse trains. The droplets are ejected so that the subsequent droplets are faster than the velocity of the droplets, and the droplets coalesce during flight to form dots on the recording medium as a single droplet (See Patent Document 1).

  However, when this method is used, the shape of the continuous electric pulse is complicated, and it is necessary to sequentially change the driving cycle of the pressure generating means, which is a transducer, and the clock signal is also complicated. In addition, since a plurality of droplets are combined to form a pixel, a small droplet that can be ejected from a nozzle is not used as a dot, so that the print resolution originally possessed by the head cannot be fully utilized.

  In view of these problems, the period of the Helmholtz natural oscillation is selected as the pulse width of a single pulse, and the time of 1/5 to 1/4 or less of the pulse width is set as the pause time. Has been proposed in which multi-pulses are alternately repeated to vary the dot diameter when landed on a recording medium (see Patent Document 2).

  However, the droplets formed by two continuous pulses are merged during the flight, but the droplets formed by the third pulse and thereafter are merged on the recording medium without being merged. Furthermore, as can be seen from FIG. 9 of Patent Document 2, the subsequent droplets are driven so that the distance from the head increases as the flight distance increases. This is good when the recording speed is slow, but when the scanning speed of the recording head is increased to increase the recording speed, or when the recording medium is transported at a high speed with the head fixed, if the subsequent droplet speed is slow, After the liquid droplets land on the recording medium, they land on the recording medium with a delay, and thus do not form a round dot shape. In the worst case, it could be a skewered dot shape or a completely separate dot. That is, there arises a problem that the recording speed cannot be improved because the print quality is deteriorated.

Japanese Patent Publication No. 7-108568

JP 2000-135800 A

  The present invention has been made in view of such problems, and an object of the present invention is to reduce the full width of the electric pulse applied to the pressure generating means in a driving method for controlling the amount of ink droplets by multi-pulse driving. By applying almost the same electric pulse waveform without making it extremely long, the continuously ejected liquid droplets land almost as a single liquid droplet before reaching the recording medium, An object of the present invention is to provide a driving method capable of dot gradation recording in a stable and high driving frequency range.

  The present invention comprises pressure generating means that operates by applying an electric pulse, and the pressure generating means discharges droplets from a nozzle opening hole that communicates with a pressure chamber that contains liquid, In the on-demand ink jet recording head having at least an expansion step for expanding the volume of the pressure chamber and a contraction step for contracting the pressure chamber and discharging droplets, the electric pulse uses at least two or more continuous electric pulses. In the case of discharging droplets, each electric pulse has the same waveform shape, and the time for the meniscus of the nozzle opening hole drawn in the pressure chamber expansion step to reach the lowest point is Tm. The time Tp from the start of the expansion step of the electric pulse to immediately before the start of the contraction step is made substantially equal to Tm, and the full width PW of the electric pulse is The total period of electrical pulses that are less than the natural period Tcxn (n is a natural number) determined by the ink flow path from the nozzle opening to the pressure chamber, and the total period of the continuous electric pulse is in the range near the natural period Tcxn. It is characterized by.

  When the relationship between the time Tm until the meniscus of the nozzle opening hole reaches the lowest point, the full width PW of the electric pulse, and the natural vibration period Tc is Tm <PW <Tc, the total of the electric pulses The variable n of the cycle Tcxn is 1 or more, and the variable n when Tm> Tc is 2 or more.

  The time Tp from the start of the electric pulse expansion process to just before the start of the contraction process is 0.7 to 1.2 times the time Tm for the meniscus of the nozzle opening hole to reach the lowest point. It is characterized by that.

  When the horizontal axis is the driving frequency of a single electric pulse and the vertical axis is the speed calculated from the time that the ink droplet ejected thereby passes between a predetermined amount of gaps, the frequency characteristic curve is taken. In addition, the repetition period of the electric pulse in the multi-pulse driving is in the vicinity of the natural period Tcxn and has a speed higher than the speed of the ink droplet in the driving of a single electric pulse of 2 kHz or less. .

  Further, the electric pulse has a holding step between the contraction step and immediately after the end of the expansion stroke.

  Furthermore, the present invention has pressure generating means that operates by application of an electric pulse, and the pressure generating means discharges droplets from a nozzle opening hole that communicates with a pressure chamber that contains liquid. In the on-demand ink jet recording head, the electrical pulse includes at least an expansion process for expanding the volume of the pressure chamber and a contraction process for contracting the pressure chamber and discharging droplets. In the case of ejecting droplets using the above, each electric pulse has the same waveform shape, and the voltage ratio between the voltage Vp of the previous electric pulse and the voltage V (p + 1) of the next electric pulse is (Vp / V ( p + 1)) ≦ 1 (p is a natural number) and when the time for the meniscus of the nozzle opening hole drawn in the expansion step of the pressure chamber to substantially reach the lowest point is Tm, The time Tp from the start of the electric pulse expansion process to just before the start of the contraction process is made substantially equal to Tm, and the full width PW of the electric pulse is determined by the ink flow path from the nozzle opening hole to the pressure chamber. The total period of electric pulses that are less than the period Tcxn (n is a natural number) and that are continuous is a range in which the electric pulse is approximately in the vicinity of the natural period Tcxn.

  In the ink jet recording head having the above characteristics, the droplet ejected by the multi-pulse drive follows the one ink droplet whose head is substantially large and the ink droplet before reaching the recording medium. It consists of an elongated tail.

  In an on-demand ink jet recording head that discharges droplets by expanding and contracting the volume of a pressure chamber containing ink by a pressure generating means, a continuous electric pulse includes at least an expansion process for taking ink into the pressure chamber, and a pressure chamber. A contraction process that contracts and discharges droplets, and the vicinity of the time when the meniscus of the nozzle opening that is pulled in the expansion process of the pressure chamber reaches the lowest point is the pulse width until just before the start of the contraction process of the electric pulse. The full width of the electric pulse is less than the natural period determined by the ink flow path from the nozzle opening to the ink inlet, that is, the so-called Helmholtz period, and the period of the continuous electric pulse is equal to or greater than the full width PW of the electric pulse. The multi-pulse is formed in the range near the natural period Tcxn (n is a natural number). Control of only the complex waveforms repeatedly driving the electrical pulses are required. Further, the driving cycle of continuous electric pulses is always constant, and the clock signal does not need to be complicated. That is, the drive circuit can be simplified.

  In addition, since the driving cycle is continuously driven in the Helmholtz cycle, the droplet amount is selectively varied at least at a driving frequency equal to or less than the Helmholtz cycle by selectively selecting an electric pulse as necessary. It becomes possible.

  Furthermore, by selecting the Helmholtz cycle, the subsequent droplets are faster than the previous droplets, so that they can always catch up with the first droplet and fly as a single droplet. At the same time, by making the driving voltage of the electric pulse slightly higher than the driving voltage of the immediately preceding electric pulse, a single droplet is formed faster, and even if the distance to the recording medium is shortened, a plurality of liquids Landing in the state of drops can be prevented. As a result, even if the scanning speed of the recording head is increased in order to improve the recording speed, it can be landed in substantially the same droplet shape as a single pulse, and the recording speed can be improved while maintaining the print quality.

  Therefore, according to the present invention, the minimum droplet ejection of the recording head and several times the droplet ejection can be realized with one head, and at the same time, the recording speed can be improved.

  In a driving method that controls the amount of ink droplets by multi-pulse driving, continuous ejection is performed by applying substantially the same electric pulse waveform without extremely increasing the entire width of the electric pulse applied to the pressure generating means. By utilizing the relationship between the movement of the meniscus of the nozzle opening and the natural period of the recording head, the purpose of causing the formed droplet to land as a substantially single droplet before reaching the recording medium substantially, The dot gradation recording can be performed stably in the high driving frequency range.

  FIG. 1 is a cross-sectional view showing an embodiment of a multilayer ink jet recording head used in the present invention. The ink jet recording head 1 of the present invention includes a nozzle plate 10 having a plurality of nozzle opening holes 11 in at least one row, a chamber plate 20 having a communication channel 21 communicating with the nozzle opening holes 11, a restrictor 32, and a pressure. In order to greatly displace the restrictor plate 30 having the opening hole that also serves as the generation chamber 31, the diaphragm plate 40 made of a thin plate that seals the pressure generation chamber 31 and the restrictor 32, and the portion corresponding to the pressure generation chamber 31 An area for holding the diaphragm plate 40 as the vibration plate 41, a support plate 50 having an opening hole in the common ink reservoir 52, and a filter 61 for preventing foreign matter from entering the flow path to each nozzle opening hole 11 are provided. A flow path substrate 5 comprising a filter plate 60 having a flow path substrate 5, and Introducing ink from the parts, it is formed from the high-rigidity plate 70 having a common ink chamber 71 for storing. A piezoelectric actuator 80 having a piezoelectric vibrator 81 that is held by a support member 82 and divided into a plurality of pieces is inserted into the opening groove 72 opened in the high-rigidity plate 70. Abutted and fixed to the diaphragm 40.

  Here, the nozzle plate 10 is drilled with high precision in order to obtain the straightness of flying ink droplets, and is formed by a method of machining a hole by a nickel electforming method or a stainless steel thin plate by a precision press method. The chamber plate 20 is formed with a communication channel 21 whose longitudinal direction is shorter than a hole formed in the restrictor plate 30. The nozzle opening hole 11 is located on the end side of the communication channel 21. The restrictor plate 30 is provided with elongated openings serving as flow paths for the pressure generating chamber 31 and the restrictor 32. FIG. 1 shows an example in which the nozzle opening holes 11 are arranged in a line. However, even if a plurality of lines are arranged in one recording head, the nozzle opening holes 11 are located inside and the flow of the pressure generating chamber 31 and the like You may arrange | position so that a path hole may mutually oppose. The chamber plate 20 and the restrictor plate 30 are formed by processing a thin stainless steel plate by an etching method or a precision press method. Alternatively, a silicon wafer may be formed by an anisotropic etching method or a dry etching method.

  The diaphragm plate 40 for sealing the pressure generating chamber 31 and the restrictor 32 is a thin plate made of a stainless steel plate made of a thin plate or a nickel material by an electroforming method, compared to other plates. Alternatively, after laminating the thin plastic film or the plastic film and the thin metal plate, the metal plate in the region serving as the vibration plate may be removed by etching. The support plate 50 can also be formed by processing a thin stainless steel plate by an etching method or a precision press method.

  The high-rigidity plate 70 can be easily formed by cutting a stainless bar or the like. The piezoelectric actuator 80 has a bulk state piezoelectric element in which conductive materials and piezoelectric materials are alternately stacked, and is fixed to one end side of the support member 82, and a plurality of bulk piezoelectric elements are provided so as to correspond to the individual pressure generation chambers 31. The piezoelectric vibrator 81 is divided, and the end face of the piezoelectric vibrator 81 is abutted and fixed to the vibration plate 41. The piezoelectric element shown in this example is of the d33 type that is displaced most in the stacking direction, but may be of the d31 type that is displaced in the stacked vertical direction, or a method using a thin plate piezoelectric body. It may be. Alternatively, instead of the piezoelectric actuator 81, an electrostatic system may be used as the displacement conversion means.

  Next, an operation process in which ink droplets are ejected from the ink jet recording head 1 configured as described above will be described with reference to FIG. FIG. 2 shows an example of an ink jet recording head having the simplest laminated structure of thin plates. FIG. 3 is a diagram showing an example of an electric pulse used for discharging a droplet from the nozzle opening hole 11. When the electric pulse 7 is applied to the piezoelectric vibrator 81 with the predetermined potential difference V (corresponding to Tf in FIG. 3) with the ink 6 filled in the ink flow path, the piezoelectric vibrator 81 contracts, The diaphragm 41 of the diaphragm plate 40 is deformed. As a result, the volume of the pressure chamber generating chamber 31 expands, and the ink 6 is supplied from the common ink chamber 71 through the restrictor 32 to the pressure chamber generating chamber 31 (arrow B in FIG. 2B). At the same time, the ink meniscus in the nozzle opening hole 11 is also pulled back to the pressure generating chamber 31 side (arrow A in FIG. 2B). Such a process is hereinafter referred to as an expansion stroke, and the time is Tf. When the voltage is held as it is, the meniscus drawing is completed, and the meniscus tries to return to the outlet side of the nozzle opening hole 11 again. Such a process is called a holding process, and the time is Tp. Then, at approximately the time when the meniscus is about to return to the outlet side of the nozzle opening hole 11, the voltage is released in a shorter time than in the contraction in the direction in which the piezoelectric vibrator 81 expands. This process is called a contraction process, and the time is Tr. Then, the ink 6 filled in the pressure generating chamber 31 is compressed by the expansion process, and the pressure generating chamber 31 is in a high atmospheric pressure state, and the pressure of the ink 6 increases (the state of FIG. 2C). This pressure causes ink droplets 8 to fly from the nozzle opening holes 11 (state shown in FIG. 2D).

  FIG. 4 shows a laser Doppler device that observes the movement of the meniscus, which is the ink surface of the nozzle opening 11 when a weak electric pulse 9 is applied to the ink jet recording head 1 according to the present invention. It is what. The recording head 1 used for the observation was one having a nozzle opening hole 11 of 38 μm and a nozzle pitch of 0.338 mm. The electric pulse 9 applies a signal 9a for expanding the pressure generating chamber 31, and keeps the state, and when the meniscus is almost restored to its original position, a signal for releasing the expansion is given and observed. The meniscus movement is greatly drawn by the expansion of the pressure generation chamber 31. The time Tm from immediately after application of the voltage signal 9a to just before the meniscus is drawn and starts to return again, that is, the time Tm to the lowest point of the meniscus drawing is about 9 μs. Thereafter, if the expansion is kept, the meniscus starts to return to the nozzle opening hole 11 side while vibrating. The period Tc is approximately 14 to 15 μs. It is already known that this vibration indicates the natural period of this recording head.

  Next, a multi-pulse driving method for controlling the amount of ink droplets according to the present invention will be described in detail. FIG. 6 shows an example when an electric pulse is continuously applied twice to the recording head 1 in which the meniscus of FIG. 4 is observed. The time Tf for the expansion stroke of each electric pulse 100a and 100b is about 3 μs, the time Tp for the holding step is 6 μs, the time Tr for the contraction step is about 3 μs, and the total time Tw of the expansion step and the holding step is The meniscus pull-in time Tm is about 9 μs, and the total time PW of one electric pulse is 12 μs. The period of the continuous electric pulse was 14.5 μs, which is the natural period Tc of the recording head 1, that is, a driving period of about 68 kHz.

  The result of observing the flying state of the ink droplet at this time is shown in FIG. (A) to (d) of FIG. 7 are views observed by gradually shifting the time immediately before ink droplets jump out of the nozzles. As shown in the figure, with respect to the ink droplet 108a ejected by the first electric pulse 100a, the ink droplet 108b ejected by the second electric pulse 100b catches up with the previous ink droplet 8a, and in the air You can see how they merge. This is because the vibration of the internal pressure in the pressure generating chamber 31 (vibration due to the natural period) generated by the previous electric pulse 100a resonates by the second electric pulse 100b, and the pressure in the pressure generating chamber 31 further increases. This is because the ink droplet speed of the second ink droplet 108b is increased.

  FIG. 8 shows the result of analyzing the pressure fluctuation in the pressure generating chamber 31 by simulation in order to verify the phenomenon described above. FIG. 8A shows the pressure change in the vicinity of the inlet of the nozzle aperture 11 calculated by linear calculation using Wolfram Research's calculation software Mathematica (registered trademark), modeling the ink flow path. FIG. 8B shows the result of analyzing the pressure change in the pressure generation chamber 31 using the FLOW-3D (registered trademark) manufactured by Ines Corporation. Although the shape of the pressure vibration waveform is slightly different depending on a slight model difference, it has been found that in both cases, the internal pressure of the pressure generating chamber 31 generated by the electric pulse 100a is further increased by the electric pulse 100b. Thereby, it can be understood that the droplet speed of the subsequent ink droplet 8b is increased.

  FIG. 5 shows the movement of the meniscus when the time Tf of the signal 9a of the electric pulse 9 is changed. As can be seen, when the time of the signal 9a changes, the time Tm to the lowest meniscus pull-in point also changes. Naturally, the vibration period Tc in the subsequent return process is the same. That is, it can be understood that stable driving can be realized by changing Tw which is the sum of the expansion stroke time Tf and the holding process time Tp according to the time Tf. In addition, according to the experimental results, it was confirmed that Tp was (0.7 to 1.2) × Tm, and the subsequent ink droplet caught up with the immediately preceding ink droplet.

  Next, FIG. 9 shows an observation result of ink ejection when more electric pulses are continuously applied using the present invention. FIG. 9 is an observation result when the electric pulse is driven by five continuous pulses, and is a result of continuous driving at about 68 kHz which is a natural period. Note that the observation results of (a) to (g) are in time series. As shown here, the ejected ink droplets have a time difference depending on the number of applied pulses, but it can be seen that all subsequent ink droplets always catch up with the previous ink droplets. In the case of this example, it was found that they were almost integrated at a point about 2.5 mm away from the nozzle opening hole 11 (state (7)). Therefore, it can be easily determined that the subsequent ink droplets always catch up with the immediately preceding ink droplets even in continuous multi-pulse driving below this. In addition, the final droplet shape is substantially the same as the droplet shape when one electric pulse is applied. Therefore, the liquid dot when landing on the recording medium has a substantially round shape. In other words, by applying electrical pulses continuously at a natural period of about 68 kHz and selectively selecting one, three, five, etc. as necessary, dots The size can be controlled, and gradation expression is possible. Therefore, the printing quality in graphic printing such as gradation can be improved by high driving frequency, that is, high printing speed and multi-value gradation expression.

  FIG. 10 shows the observation results of ink ejection when the drive period of continuous electric pulses is about twice the natural period Tc of the recording head 1. The observation results of (a) to (h) are in time series. The shape of the electric pulse was the same as that of 100a and 100b, and five electric pulses were applied at a driving cycle of 26 μs and approximately 35 kHz. As can be seen from FIG. 10, when the flying distance of the ink droplet becomes longer, it can be seen that the subsequent ink droplet catches up. However, in the case of this example, the fifth ink droplet approached the previous ink droplet, but could not catch up even if it flew a distance of 10 mm. This is because the pressure in the pressure generation chamber 31 is gradually balanced, and the flight distance becomes long and the kinetic energy is lost, making it impossible to catch up.

  Next, a case where the natural period Tc of the recording head 1 is short (high frequency) will be described. Even with a recording head having a short natural period Tc, the time Tm to the lowest meniscus pull-in point may be longer than the natural period Tc. For example, when a recording head having a nozzle opening hole diameter of 25 μm and a nozzle pitch of 0.25 mm is used, the recording head has a natural period Tc of 8 μs (125 kHz) and a meniscus pull-in time Tm of about 9 μs. In such a case, the sum of the expansion stroke and the holding time of the electric pulse may be substantially the meniscus pull-in time Tm, and the period of the continuous electric pulse may be set to be twice or more (however, an integral multiple) of the natural period Tc.

  FIG. 11 is a diagram simulating a pressure change in the pressure generating chamber 31 when the natural period Tc of the recording head 1 described above is short (high frequency). As for the pressure change in the pressure generating chamber 31, it can be seen that the second pressure is higher as in the result shown in FIG. This indicates that the subsequent ink drop catches up with the immediately preceding ink drop. Although not shown, it was also possible to confirm that the ink droplet caught up with the immediately preceding ink droplet by the observation method as shown in FIG. In this case, even when five consecutive electric pulses were applied, the time required for the subsequent droplets to catch up as in the recording head having a long natural period Tc was short. This is because the natural period of the recording head is short, so the volume in the pressure generating chamber 31 is small, and the increase in internal pressure is large for the recording head having a long natural period. This is due to the decrease in pressure drop. As described above, the same effect as that of the recording head shown in FIG. 9 can be obtained by continuously driving the recording head 1 with a time twice as long as the natural period Tc.

  FIG. 12 shows a frequency characteristic curve of the ink droplet in which the horizontal axis represents the driving frequency of the electric pulse and the vertical axis plotted the average velocity of the ink droplet calculated from the time until the ink droplet reaches the flying distance of 1 mm. It can be seen that the speed of the ink droplet changes according to the drive frequency. The time calculated from the peak of the speed change curve is approximately the same as the natural period Tc of the recording head 1. Two continuous multi-pulse driving was performed at the points shown in (1), (2), (3), (4) and (5) in this speed curve. (1) to (5) in FIG. 13 show a state when a predetermined amount has jumped from immediately after the start of ink droplet ejection in the driving cycle corresponding to (1) to (5) in FIG. As can be seen from the frequency characteristics of the ink droplet shown in FIG. 12, the ink droplet velocity at 2 kHz is about 8 m / s, whereas the velocity from (3) to (5) is faster than 8 m / s. (1) and (2) are 8 m / s or less. As a result of the observation, it can be seen that (3) to (5) in FIG. 12 surely catch up with the immediately preceding ink droplet. In the case of (2), although it has not caught up, the distance between the ink droplets is clogged, so it seems that it will eventually catch up. And in the case of (1), it turned out that it cannot catch up reliably.

  FIG. 14 shows the result of analyzing the ejection state of ink droplets using FLOW-3D in a state in which five continuous pulses are applied at the frequency of (5) in FIG. It has been verified that the subsequent ink droplet catches up even when the number of consecutive pulses is increased. That is, in multi-pulse driving, in order to combine droplets in the air or almost immediately before reaching the recording medium, the driving cycle of multi-pulse driving is approximately the natural period Tc, and a single electric By continuously driving in the vicinity of an integral multiple of Tc in a region faster than the ink droplet velocity in the low frequency region of the frequency characteristic curve at the pulse, the ink droplet by the subsequent electric pulse catches up with the immediately preceding ink droplet. I understood. However, this effect is preferably about 2 to 3 times as the period of the multi-pulse becomes longer as the period that is an integral multiple of the natural period Tc is longer, and the effect of catching up with the immediately preceding ink droplet is lessened.

  From the above, in the multi-pulse drive, when the ink droplet amount is controlled and the dot size is variably controlled, the drive cycle of the continuous electric pulse takes the vicinity of the natural cycle Tc of the recording head 1 and a single electric drive. By performing multi-driving in a region larger than the ink droplet velocity in the pulse, it is possible to provide an ink jet recording head that can be driven at a high frequency and can perform multi-pulse driving without reducing the printing speed.

  As described above, it has been found that as the number of pulses in multi-pulse driving increases and the driving cycle becomes longer, the time and distance until they are combined increases. FIG. 15 is a diagram in which the meniscus of the ink in the nozzle opening hole 11 is observed when the drive voltage is lowered to the extent that ink droplets are not ejected and five electric pulses are continuously applied. As can be seen from the figure, the meniscus protrusion amount after the fourth continuous electric pulse does not increase so much. That is, as the number of continuous electric pulses increases, the pressure in the pressure generating chamber 31 becomes an equilibrium state.

  Therefore, as shown in FIG. 16, by gradually increasing the driving voltage of the continuous electric pulse as it follows, it becomes possible to catch up with the immediately preceding ink droplet faster. For example, when the voltage of the first electric pulse is V1, the second is V2 = V1 × 1.1, the third is V3 = V × 1.2, and the fourth is V4 = V1 × 1.3. Thus, it is not necessary to increase it continuously, and V (p + 1) ≧ V (p) with respect to the driving voltage of the immediately preceding electric pulse, and (Vp / V (p + 1)) ≦ 1 (p is the voltage ratio) Natural number). For example, in the example shown in FIG. 15, the drive voltage of the fourth electrical pulse is made higher than the drive voltage of the immediately preceding electrical pulse, thereby catching up with the ink droplet ejected immediately before. Further, the period of the multi-pulse drive is gradually increased in a range of an area near the integer multiple of the natural period Tc shown in the frequency characteristic curve shown in FIG. 12 and faster than the speed of the single electric pulse in the low frequency range. It can be understood that even if the multi-pulse driving cycle is shortened, the subsequent ink droplet catches up with the immediately preceding ink droplet. In this way, by increasing the speed of the subsequent ink droplets, it is possible to accelerate the coalescence of the ink droplets in the air, and it is not necessary to increase the distance to the recording medium. As a result, since the wind is flying, the factors that deteriorate the straightness of the ink droplets due to disturbance are reduced, the ink droplet landing position accuracy is increased, and the printing quality can be improved.

  In the invention described above, as shown in FIG. 17, the shape of the electric pulse is a step of expanding the pressure generating chamber 31, a holding step, and a step of contracting (or restoring) the pressure generating chamber 31. The same effect can be obtained by adding a restoring step for restoring the original position again after the shrinking step is further shrunk from the normal position.

  According to the ink jet recording head of the present invention, it is possible to control a small droplet to a large droplet with a high driving frequency from a single nozzle, enabling high-speed printing and obtaining high-definition print quality. This makes it possible to expand applications from office use printing devices to industrial printing fields.

FIG. 3 is a cross-sectional view showing a recording head used in the present invention. FIG. 4 is a model diagram illustrating an operation process when ink droplets are ejected in the present invention. 2 is an example of an electrical pulse for a single ink drop. It is a graph which shows the result of having observed the displacement of the ink meniscus of a nozzle opening hole. It is the graph which observed the meniscus when changing time Tf of an electric pulse. It is an example of the continuous electric pulse used in this invention. It is the figure which observed the mode of the ink droplet ejected from the recording head when it drives with the electric pulse of FIG. 6 is a graph showing a result of simulation calculation of pressure fluctuation in a pressure generation chamber of a recording head. FIG. 6 is a diagram of an observation of ink droplet ejection when the recording head is driven with five continuous electric pulses. FIG. 6 is a diagram of an ink droplet ejection state observed when the recording head is driven with five continuous electric pulses and the drive frequency is driven at approximately twice the natural period. It is the graph which calculated the pressure fluctuation in the pressure generation chamber at the time of the continuous pulse drive used as another Example. FIG. 4 is a diagram illustrating frequency characteristics of a recording head. It is the figure which observed the mode of ejection of the ink drop in each point shown in FIG. It is the figure which collated the state of the ejection of the ink droplet of 5 continuous multi-drives by calculation. It is the graph which observed the mode of the meniscus in a nozzle opening hole by 5 continuous multi drive. It is a figure which shows the example used as the other Example of the continuous electric pulse. FIG. 6 shows another implementation of a single electrical pulse in multi-drive.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording head 5 Flow path board | substrate 7 Electric pulse 8 Ink droplet 9 Electric pulse 10 Nozzle plate 11 Nozzle opening hole 20 Chamber plate 21 Communication flow path 30 Restrictor plate 31 Pressure generating chamber 32 Restrictor 40 Diaphragm plate 41 Diaphragm plate 50 Support plate 52 Common ink reservoir 60 Filter plate 61 Filter 70 High rigidity plate 71 Common ink chamber 72 Opening groove 80 Piezoelectric actuator 81 Piezoelectric vibrator

Claims (7)

A pressure generating means that operates by application of an electric pulse, wherein the pressure generating means discharges a droplet from a nozzle opening hole that communicates with a pressure chamber containing a liquid, and the electric pulse is at least In an on-demand ink jet recording head having an expansion step of expanding the volume of the pressure chamber, and a contraction step of contracting the pressure chamber and discharging droplets,
When droplets are ejected using at least two or more continuous electric pulses, each electric pulse has the same waveform shape, and the meniscus of the nozzle opening hole drawn in the expansion step of the pressure chamber is almost equal. When the time to reach the lowest point is Tm, the time Tp from the start of the electric pulse expansion process to just before the start of the contraction process is made substantially equal to Tm, and the full width PW of the electric pulse is set to the nozzle opening hole. The total period of electric pulses that are less than the natural period Tcxn (n is a natural number) determined by the ink flow path from the pressure chamber to the pressure chamber is such that the electric pulse is in the range near the natural period Tcxn. To drive an inkjet recording head.   When the relationship between the time Tm until the meniscus of the nozzle opening hole reaches the lowest point, the full width PW of the electric pulse and the natural vibration period Tc is Tm <PW <Tc, the total period Tcxn of the electric pulse 2. The ink jet recording head driving method according to claim 1, wherein the variable n is 1 or more, and the variable n when Tm> Tc is 2 or more.   The time Tp from the start of the electric pulse expansion process to just before the start of the contraction process is 0.7 to 1.2 times the time Tm for the meniscus of the nozzle opening hole to reach the lowest point. The method of driving an ink jet recording head according to claim 1.   The repetition period of at least two or more consecutive electrical pulses is in the vicinity of the natural period Tcxn and having a speed greater than the speed of ink droplets when driven at 2 kHz or less of a single electrical pulse. Item 3. A method for driving an ink jet recording head according to Item 1 or 2.   5. The method of driving an ink jet recording head according to claim 1, wherein the electric pulse has a holding step between the contracting step and immediately after the end of the expansion stroke. 6. A pressure generating means that operates by application of an electric pulse, wherein the pressure generating means discharges a droplet from a nozzle opening hole that communicates with a pressure chamber containing a liquid, and the electric pulse is at least In an on-demand ink jet recording head having an expansion step of expanding the volume of the pressure chamber, and a contraction step of contracting the pressure chamber and discharging droplets,
When droplets are ejected using at least two or more continuous electric pulses, each electric pulse has the same waveform shape, and the voltage Vp of the previous electric pulse and the voltage V (p + 1) of the next electric pulse are The voltage ratio is set to (Vp / V (p + 1)) ≦ 1 (p is a natural number), and the time required for the meniscus of the nozzle opening hole drawn in the expansion process of the pressure chamber to reach the lowest point is Tm. The time Tp from the start of the electric pulse expansion process to just before the start of the contraction process is made substantially equal to Tm, and the full width PW of the electric pulse is determined by the ink flow path from the nozzle opening hole to the pressure chamber. The total period of the electric pulses that are less than the natural period Tcxn (n is a natural number) and that is continuous is a range in the vicinity of the natural period Tcxn. Driving method of the recording head. When a plurality of droplets are ejected by using at least two continuous electric pulses, before reaching the recording medium, one leading ink droplet follows the ink droplet. The method of driving an ink jet head according to any one of claims 1 to 6, wherein an elongated tail portion is formed.

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