JP5315540B2 - Inkjet recording device - Google Patents

Description

  The present invention relates to an ink jet recording apparatus, and more particularly to landing position adjustment when ejecting ink droplets of a plurality of sizes from one nozzle.

  2. Description of the Related Art An apparatus for recording dots by forming ink droplets and flying them onto an image recording medium has been put to practical use as an ink jet printer. In recent years, the demand for the recording quality of this ink jet recording apparatus has increased, and various printing performances such as high image quality, high resolution, and high speed will be required in the future. Yes.

  In general, gradation control methods include thinning out dots to be recorded, that is, modulating the area by expressing the density by reducing the recording density of the dots, and controlling the dot diameter by ejecting droplets multiple times to the same part. And a method using a plurality of inks having different shades.

  Here, the area modulation is a method of expressing shades by thinning out the dots to be recorded, that is, by reducing the recording density of the dots. Therefore, when performing multi-tone printing, there is a problem that the printing resolution is lowered. is there. Further, in the method of ejecting droplets a plurality of times on the same portion, there is a problem that the printing speed is lowered because a printing operation is performed a plurality of times at the same position in order to increase the number of gradations. In addition, the method using a plurality of inks has problems such as an increase in cost and an increase in the size of the apparatus.

  As a technique for solving these problems and realizing multi-tone printing, there is a dot modulation method. Dot modulation is a method of expressing light and shade by changing the amount of ink ejected. In the ink jet recording apparatus, the ink jet head includes a nozzle that ejects ink droplets, a pressure generation chamber that communicates with the nozzle, and an actuator unit that generates energy to pressurize the ink in the pressure generation chamber. By supplying a driving pulse for ejecting the ink droplet size corresponding to the gradation to the means, it is possible to eject ink droplets of different sizes.

  By the way, when the applied voltage of the drive pulse is changed as a method of changing the ink droplet size, the ejection speed increases as the ink droplet size increases, and the landing position on the recording medium varies depending on the ink droplet size. End up.

  Therefore, as a method of aligning the landing position while making the ink droplet size variable, in Patent Document 1, the drive pulse is set so that a plurality of ink droplets ejected from the nozzles are combined during the flight, The final drive pulse, which is one, is such that the ejection speed of the ink droplets ejected by the final drive pulse is slower than the ejection speed of the ink droplets ejected by the other drive pulses. It is set to accumulate the volume of.

JP 2007-144659 A

  However, in the invention described in Patent Document 1, since the ink droplets ejected by the final drive pulse have desired characteristics, it is necessary to generate a special waveform, resulting in a complicated circuit.

  An object of the present invention is to provide an ink jet recording apparatus capable of aligning the landing position accuracy on a recording medium even when ink droplets of a plurality of sizes are ejected.

In order to achieve the object, the invention according to claim 1 includes a nozzle for ejecting ink, a pressure chamber communicating with the nozzle, and a pressure generating element for changing the volume of the pressure chamber, and includes a Helmholtz resonance period Tc. in the ink jet recording apparatus comprising an ink jet head to form an image by depositing a drive pulse for ejecting ink droplets onto a recording medium by ejecting ink droplets from the nozzle by applying to the pressure generating element having,
A pre-driving pulse having a first waveform shape that does not eject ink droplets, and a driving pulse having a second waveform shape that ejects ink droplets, and the interval between the pre-driving pulse and the driving pulse is Helmholtz resonance The period is approximately 3/2 Tc. When only one driving pulse is applied, the preliminary driving pulse is not applied, and when at least two driving pulses are applied at a predetermined interval, the preliminary driving is performed. A plurality of the driving pulses are applied after the pulses are applied, and ink droplets corresponding to the number of the driving pulses are combined .

The invention described in claim 2 is characterized in that, in the invention described in claim 1, the first waveform shape and the second waveform shape are trapezoidal waves, and applied voltages are different .

  The present invention is configured as described above, and even when ink droplets of a plurality of sizes are ejected, the landing position accuracy on the recording medium can be made uniform.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the structure of the inkjet head used in this embodiment will be described.

  2 to 4 are diagrams showing details of the on-demand type head part, FIG. 2 is an exploded perspective view of the head part, FIG. 3 is a sectional view after the head part is assembled, and FIG. 4 is a sectional view taken along the line AA in FIG. FIG.

  In these drawings, reference numeral 1 is an orifice, 2 is an orifice plate, 3 is a pressure chamber, 4 is a pressure chamber plate, 5 is a restrictor, 6 is a restrictor plate, 7 is a diaphragm, 8 is a filter, 9 is a diaphragm frame plate, 10 is a hole, 11 is a support plate, 12 is a common liquid passage, 13 is a housing, 20 is an adhesive, 21 is a piezoelectric actuator, 22 is a piezoelectric vibrator, 23 is an external electrode, 24 is a conductive adhesive, 25 is A support substrate, 26 is an individual electrode, 27 is a common electrode, 28 is a through hole, and 29 is a liquid introduction pipe.

  As shown in FIG. 2, the on-demand type head portion is composed of an orifice plate 2, a pressure chamber plate 4, a restrictor plate 6, a diamond frame plate 9, a support plate 11, a housing 13, a piezoelectric actuator 21, and the like. .

  The orifice plate 2 in which a large number of orifices 1 are formed in a row is manufactured by a nickel material electroforming method, a precision pressing method such as a stainless steel material, or a laser processing method. A number of pressure chambers 3 corresponding to the orifice 1 are formed in the pressure chamber plate 14 and communicated with the orifice 1. As shown in FIG. 3, the restrictor plate 6 is formed with a restrictor 5 that communicates the common liquid passage 12 and the pressure chamber 3 and controls the amount of liquid flowing into the pressure chamber 3. The pressure chamber plate 4 and the restrictor plate 6 are manufactured by a stainless steel material etching method or a nickel material electroforming method.

  A diaphragm 7 for efficiently transmitting the pressure of the piezoelectric vibrator 22 to the pressure chamber 3 and a filter 8 for removing dust in the liquid flowing into the restrictor 5 from the common liquid passage 12 are formed on the diamond frame plate 9. ing. The diamond frame plate 9 is manufactured by a stainless steel material etching method or a nickel material electroforming method.

  When the support plate 11 fixes the diaphragm 7 and the piezoelectric vibrator 22 with the adhesive 20, the support plate 11 regulates the position of the vibration system fixing end of the diaphragm 7, and the adhesive protruding from the bonding portion spreads on the diaphragm 7. A restricting hole 10 is formed. The support plate 11 is manufactured by a stainless steel material etching method or a nickel material electroforming method. A housing 13 made of metal or synthetic resin is provided with a common liquid passage 12, and an ink supply pipe or a head connection pipe (not shown) is connected to the common liquid passage 12.

  The ink supplied from the ink supply pipe or the head connection pipe passes through the filter 8 in the middle of the common liquid passage 12 of the head, and flows in order to the restrictor 5, the pressure chamber 3, and the orifice 1. By applying a predetermined drive pulse between the individual electrode 26 and the common electrode 27, the piezoelectric vibrator 22 expands and contracts. When the application of the drive pulse is stopped, the piezoelectric vibrator 22 returns to the state before the expansion and contraction. Due to such deformation of the piezoelectric vibrator 22, pressure is instantaneously applied to the ink in the pressure chamber 3, and the ink droplets from the orifice 1 land on the recording medium.

  The ink jet head configured as described above has a Helmholtz resonance period governed by compliance and inertance determined by the shapes of the nozzle opening, the ink supply port, and the pressure generating chamber.

  FIG. 5 is a characteristic diagram showing the relationship between the printing cycle and the ink droplet velocity when one drive pulse is applied in one printing cycle. As shown in the figure, the ink droplet velocity varies depending on the ink droplet ejection cycle. To do. The ink-jet head used in this example has a Helmholtz period of approximately 7.6 us, and exhibits an ink droplet velocity peak in the vicinity of an integral multiple of the Helmholtz period.

  Here, in order to eject ink droplets of a plurality of sizes, a number of drive pulses corresponding to the desired size are applied at a predetermined interval within one printing cycle, and ink droplets corresponding to the number of drive pulses are ejected. However, by setting the interval between the drive pulses to a value close to the Helmholtz period, the ink droplets can be combined during flight to form one ink droplet and then land on the recording medium.

  FIG. 6 shows the relationship between the number of drive pulses and the weight of the ink droplet when the ink droplets are combined while flying by the above method, and FIG. 7 shows the relationship between the number of drive pulses and the ink droplet velocity. As shown in FIG. 6, by increasing the drive pulse, the ink droplet weight can be increased almost directly. However, since it is necessary to collide with the previously ejected ink droplet during the flight, the speed of the second shot is larger than the number of the first shot in the case of the drive pulse number 2, and the combination of the drive pulse number 1 is caused by the coalescence. Ink droplet speed increases. When the number of driving pulses is 3, the ink droplet speed of the third shot is even higher, so that the ink droplet speed becomes higher than that when the number of driving pulses is 2 due to coalescence. Therefore, as shown in FIG. 7, the ink droplet speed increases as the number of drive pulses increases.

  As a countermeasure for the above problem, the present invention uses the print signal and the drive signal shown in FIG. The drive signal has a preliminary drive pulse P0 and drive pulses P1, P2, P3, and P4. Waveforms P1, P2, P3, and P4 are the same trapezoidal wave, and P0 is different only in voltage. Since the preliminary drive pulse P0 is a waveform for controlling the ink meniscus of the nozzle, it is necessary to set a voltage at which ink is not ejected. In this embodiment, the voltage V0 is set to ½ times V1.

The print signal is a signal for selecting a drive pulse in the drive signal according to the print information. The print signal S1 for selecting one drive pulse selects only the drive pulse P1, and the print signal S2 for selecting two drive pulses is Preliminary drive pulse P0 and drive pulses P1 and P2, print signal S3 for selecting three drive pulses is preliminary drive pulse P0, drive pulses P1, P2 and P3, and print signal S4 for selecting four drive pulses is preliminary drive pulse P0. And drive pulses P1, P2, P3 and P4 are selected. The interval T0 between the pre-driving pulse P0 and the driving pulse P1 is the same as the ink droplet speed when the second ink droplet collides with the first ink droplet and ejected by only the driving pulse P1. In order to reduce the droplet speed of the drive pulse P1, the Helmholtz period is set to about 3/2 times. In this embodiment, 12.0 us. Each drive pulse interval catches up with the previously ejected ink droplet and suppresses an increase in the ink droplet velocity as much as possible. In this embodiment, the drive pulse interval is closer to the Helmholtz cycle than T0 but larger than the Helmholtz cycle, and T1 = 9.1us, T2 = 9.7us, T3 = 9.5us. That is, when the interval T0 between the preliminary drive pulse and the drive pulse, the Helmholtz period of the inkjet head is Tc, and the intervals between the drive pulses are T1, T2, ... Tn-2, Tn-1 (n is an integer),
Tc ≦ T1, T2,... Tn-2, Tn-1 <T0
It is recommended to set the conditions to satisfy.

  FIG. 8 shows the relationship between the number of drive pulses and the ink droplet weight when the ink droplets are combined while flying under the above conditions, and FIG. 9 shows the relationship between the number of drive pulses and the ink droplet velocity. As shown in FIG. 8, as in the case where there is no preliminary drive pulse, by increasing the drive pulse, the ink droplet weight can be increased almost directly. Further, by adding the preliminary drive pulse, as shown in FIG. 9, the problem that the ink droplet speed increases with the number of drive pulses can be solved.

  In addition, the said embodiment is a suitable embodiment of this invention, and does not limit the range of this invention only to the said embodiment, In the form which gave various change in the range which does not deviate from the summary of this invention. Can be implemented.

It is a figure which shows the drive signal and print signal which concern on embodiment of this invention. It is a disassembled perspective view of the inkjet head which concerns on embodiment of this invention. It is sectional drawing of the inkjet head. It is sectional drawing on the FIG. 3A-A line. FIG. 6 is a characteristic diagram illustrating a relationship between a printing cycle and an ink droplet speed. FIG. 10 is a characteristic diagram showing the relationship between the number of drive pulses and the ink droplet weight when a preliminary drive pulse as a conventional example is not used. FIG. 10 is a characteristic diagram showing the relationship between the number of drive pulses and the ink droplet velocity when a preliminary drive pulse as a conventional example is not used. FIG. 6 is a characteristic diagram showing a relationship between the number of drive pulses and the ink droplet weight according to the embodiment of the present invention. FIG. 6 is a characteristic diagram showing the relationship between the number of drive pulses and the ink droplet velocity according to the embodiment of the present invention.

Explanation of symbols

  1: orifice, 2: orifice plate, 3: pressure chamber, 4: pressure chamber plate, 5: restrictor, 6: restrictor plate, 7: diaphragm, 8: filter, 9: diamond frame plate, 10: hole, 11 : Support plate, 12: Common liquid passage, 13: Housing, 20: Adhesive, 21: Piezoelectric actuator, 22: Piezoelectric vibrator, 23: External electrode, 24: Conductive adhesive, 25: Support substrate, 26: Individual Electrode, 27: Common electrode, 28: Through hole, 29: Liquid introduction pipe.

Claims (2)

A nozzle for ejecting ink and a pressure chamber communicating with the nozzle, a pressure generating element for varying the volume of the pressure chamber, provided with an inkjet head having a Helmholtz resonance period Tc, the drive pulse for ejecting an ink droplet in the ink jet recording apparatus which forms an image by depositing on the recording medium by ejecting ink droplets from the nozzle by applying to the pressure generating element,
A preliminary drive pulse having a first waveform shape that does not eject ink droplets, and a drive pulse having a second waveform shape that ejects ink droplets;
The interval between the preliminary drive pulse and the drive pulse is approximately 3/2 Tc of the Helmholtz resonance period,
When only one drive pulse is applied, the preliminary drive pulse is not applied,
When at least two of the drive pulses are applied at a predetermined interval, a plurality of the drive pulses are applied after the preliminary drive pulse is applied, and ink droplets corresponding to the number of the drive pulses are combined. an ink jet recording apparatus characterized by the. 2. The ink jet recording apparatus according to claim 1, wherein the first waveform shape and the second waveform shape are trapezoidal waves, and different voltages are applied .

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