JP3984583B2 - Inkjet head and inkjet printer - Google Patents

Description

  The present invention relates to an inkjet head and an inkjet printer.

  In the prior art, a shear mode in which image formation is performed by selectively ejecting ink from ejection nozzles provided in each pressure chamber by changing the volume of the pressure chamber by a pressurizing unit that generates shear strain in accordance with an electrical signal. A type of inkjet head is known (for example, see Patent Document 1). Such a shear mode type ink jet head has a feature that the pressure chambers are easily arranged at high density.

  However, the above-described shear mode type ink jet head has a problem that a phenomenon called crosstalk in which a pressure change in one pressure chamber changes the pressure or flow velocity of ink in another nearby pressure chamber occurs. Crosstalk is considered to occur because the pressure of the ink in the pressure chamber displaces the partition wall between the pressure chambers and changes the ink pressure in the adjacent and adjacent pressure chambers.

  By the way, in the pressure chambers located at both ends in the printing range, only crosstalk from other pressure chambers located inside the printing range acts, whereas in the pressure chambers located inside the printing range, both sides. Crosstalk from the other pressure chambers located acts. For this reason, the influence of crosstalk differs between the pressure chambers located inside the pressure chambers located at both ends in the printing range. Thus, the volume of ink droplets ejected from the ejection nozzles communicated with the pressure chambers located at both ends in the printing range and the ink ejected from the ejection nozzles communicated with the pressure chambers located inside the printing range Unlike the volume of the droplets, density unevenness and image quality deterioration are likely to occur in the printed matter.

  As an ink jet head that attempts to equalize the influence of crosstalk acting on each pressure chamber, there is an ink jet head as shown in FIG. 13 (see, for example, Patent Document 2). The ink jet head shown in FIG. 13 forms three dummy pressure chambers 102 on each side of the effective pressure chambers 101 arranged in a plurality within the printing range, and one discharge nozzle 103 in each effective pressure chamber 101. A plurality of dummy nozzles 104 are respectively connected to the dummy pressure chambers 102. Here, the “dummy pressure chamber” refers to a pressure chamber in which ink is not ejected even when a drive signal is applied.

  In the ink jet head as shown in FIG. 13, for example, when the ink droplet is ejected by changing the volume of the effective pressure chamber 101a located at the end within the printing range, the dummy pressure chamber 102a is the same as the ink droplet ejection. Change the volume as follows. In addition, when the ink droplet is ejected by changing the volume of the effective pressure chamber 101b located at the end within the printing range, the volume of the dummy pressure chamber 102b is also changed in the same manner as the ink droplet is ejected. Further, when ink droplets are ejected by changing the volume of the effective pressure chamber 101c located at the end within the printing range, the volume of the dummy pressure chamber 102c is also changed in the same manner as the ink droplets are ejected.

  Thereby, with respect to the effective pressure chambers 101a, 101b, and 101c positioned at the end portion in the printing range, the influence of crosstalk from other pressure chambers (effective pressure chamber and dummy pressure chamber) positioned on both sides thereof is reduced. These effective pressure chambers 101a, 101b, and 101c can be operated in the same manner as other effective pressure chambers located inside.

US Pat. No. 4,879,568 JP 2000-135787 A

  However, in the ink jet head as shown in FIG. 13, when the number of dummy nozzles 104 communicating with one dummy pressure chamber 102 is plural and the volume of the dummy pressure chamber 102 is changed, ink droplets are discharged from the dummy nozzle 104. I try not to discharge.

  Therefore, the combined fluid impedance of the plurality of dummy nozzles 104 acting on the dummy pressure chamber 102, that is, the viscosity resistance and inertial resistance of the combined ink of the plurality of dummy nozzles 104 are inversely proportional to the number of dummy nozzles 104. Will drop. As a result, the main acoustic resonance frequency of the ink in the dummy pressure chamber 102 is different from the main acoustic resonance frequency of the ink in the effective pressure chamber 101.

  Here, the main acoustic resonance frequency refers to a pressure wave generated in the ink in the pressure chamber when the pressure chamber is driven by applying a voltage by the pressurizing means and the pressure wave is generated. Is the frequency at which the largest pressure oscillation is superimposed, and is also called the Helmholtz resonance frequency.

  For this reason, when a drive signal having a waveform that matches the acoustic frequency characteristics of the ink in the effective pressure chamber 101 is applied to the ink in the dummy pressure chamber 102, an abnormal pressure fluctuation occurs in the dummy pressure chamber 102, and within the printing range. In each of the three effective pressure chambers 101a, 101b, and 101c located at both ends, crosstalk caused by abnormal pressure fluctuations generated in the dummy pressure chamber 102 is received. There is a problem that the quality deteriorates.

  An object of the present invention is to provide an ink jet head and an ink jet printer that can prevent the volume of ink droplets ejected from the respective ejection nozzles from being varied due to crosstalk and prevent the occurrence of density unevenness and image quality degradation. Is to provide.

The present invention is provided in a plurality of pressure chambers arranged in parallel on a straight line across a partition wall and respectively communicating with an ink supply path, and the pressure chambers located within a printing range among the pressure chambers. a discharge nozzle, a pressurizing means for varying the volume of the pressure chamber in response to the drive signal, and respectively communicate with said pressure chamber and the outside, located outside the printable area of the pressure chamber, the previous SL ejection nozzle It has a set shape such that the fluid impedance is substantially the same, and a dummy nozzle which ink is not ejected in Rukoto opening diameter of the pressure chamber side is set smaller than the opening diameter of the outer side, the pressure selectively the by supplying to the pressure chamber located within the print range the drive signal for simultaneously varying the volume of the pressure chamber at the N-1 (natural number N ≧ 1) every interval to means varying the volume of the pressure chamber That a head driving means, when solid printing, the pressure located outside N-th print range from said pressure chamber located at the end of the print range of the pressure chamber varying the volume simultaneously by the driving signal Head driving means adapted to vary the volume of the chamber.

  According to the present invention, when driving the pressure chamber located at the end portion in the printing range, the pressure chamber located outside the printing range is driven at the same time, so that no ink is ejected from the dummy nozzle. Almost the same crosstalk as the pressure chamber located inside the printing range can be applied to the pressure chamber located at the end. As a result, the volume of ink droplets from the discharge nozzle located at the end within the printing range can be made substantially the same as the volume of ink droplet from the discharge nozzle located within the printing range. Density unevenness can be eliminated.

  An embodiment for carrying out the present invention will be described with reference to FIGS. FIG. 1 is a longitudinal side view showing an inkjet head according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AA in FIG.

  As shown in FIGS. 1 and 2, the inkjet head 1 of the present embodiment includes two piezoelectric members (a lower piezoelectric member 2 and an upper piezoelectric member 3) that are polarized in the thickness direction. The two piezoelectric members 2 and 3 are bonded together with the same poles facing each other. The bonded piezoelectric members 2 and 3 are fixed to a substrate 4 made of an unpolarized low dielectric constant piezoelectric member.

  A plurality of grooves 5 are formed in parallel at equal intervals in the substrate 4 and the piezoelectric members 2 and 3 fixed to the substrate 4. The plurality of grooves 5 are processed using a diamond cutter or the like.

  A top frame 6 is bonded to the upper surface of the substrate 4. This top plate frame 6 seals a part of the upper surface of the groove 5. Thereby, the pressure chamber 7 (7a, 7b, 7c, ...) is formed.

  A partition wall 8 (8a, 8b, 8c) is formed between the adjacent pressure chambers 7 and includes a lower piezoelectric member 2 and an upper piezoelectric member 3, and forms a pressurizing unit that varies the volume of the pressure chamber 7 in accordance with a drive signal. ,...

  An ink supply path 9 communicating with all the pressure chambers 7 is formed in the top plate frame 6.

  A top plate 10 is bonded to the top surface of the top plate frame 6. An ink supply port 11 communicating with the ink supply path 9 is formed in the top plate 10. An ink supply pipe (not shown) for supplying ink to the inkjet head 1 is connected to the ink supply port 11.

  On the inner surface of each groove 5, electrodes 12 (12a, 12b, 12c,...) That are electrically independent from each other are provided. The electrode 12 of the present embodiment is formed by electroless plating. Each electrode 12 is connected to a driver IC (not shown) which is a head driving means via a flexible cable 13 connected to the rear end of the substrate 4.

  A polyimide nozzle plate 14 is bonded to the front side of the pressure chamber 7. The nozzle plate 14 is provided with discharge nozzles 15 (15e, 15f, 15g,...) And dummy nozzles 16 (16a, 16b, 16c, 16d). The discharge nozzle 15 and the dummy nozzle 16 of the present embodiment are formed by laser processing. Laser processing of the discharge nozzle 15 and the dummy nozzle 16 with respect to the nozzle plate 14 is performed after the nozzle plate 14 is bonded to the front side of the pressure chamber 7.

  The discharge nozzle 15 is formed at a position facing the pressure chamber 7 (7e, 7f, 7g,...) Located within the printing range. The dummy nozzle 16 is formed at a position facing the pressure chamber 7 (7a, 7b, 7c, 7d) located outside the printing range.

  FIG. 2 illustrates only one end side of the inkjet head 1, and four pressure chambers 7 located outside the printing range on the other end side of the inkjet head 1, and the pressure chambers thereof. And four dummy nozzles 16 located opposite to 7 are formed.

  Ink is injected into the inkjet head 1 from the ink supply port 11 through the ink supply pipe, and is filled in the ink supply path 9, the pressure chamber 7, the discharge nozzle 15, and the dummy nozzle 16.

  In the inkjet head 1 having such a configuration, for example, when a positive drive signal is given from the driver IC to the electrode 12e, an electric field perpendicular to the polarization direction is generated in the partition walls 8d and 8e. As shown in FIG. 3, the partition walls 8d and 8e are bent in directions opposite to each other in the direction of increasing the volume of the pressure chamber 7e due to an inverse piezoelectric effect caused by an electric field orthogonal to the polarization direction, thereby generating shear strain. As a result, the volume of the pressure chamber 7e is increased (FIG. 3A). Conversely, when a negative drive signal is applied to the electrode 12e from the driver IC, the volume of the pressure chamber 7e is reduced (see FIG. 3B). Thus, the volume of the pressure chamber 7e can be selectively varied by giving a drive signal to the electrode 12e. In the pressure chamber 7e, when the volume of the pressure chamber 7e increases, the pressure of the ink in the pressure chamber 7e decreases, and pressure oscillation starting with a negative polarity occurs in the ink in the pressure chamber. Further, in the pressure chamber 7e, when the volume of the pressure chamber 7e decreases, the pressure of the ink in the pressure chamber 7e increases, and a pressure vibration starting with a positive polarity occurs in the ink in the pressure chamber 7e. The ink in the pressure chamber 7e is ejected from the ejection nozzle 15e as ink droplets when these pressure vibrations overlap and the pressure of the ink in the pressure chamber 7e increases.

  Next, the dummy nozzle 16 and the discharge nozzle 15 will be described. FIG. 4 is a cross-sectional view showing the shapes of the dummy nozzle 16 and the discharge nozzle 15. The dummy nozzle 16 has a shape in which the diameter in the nozzle widens in the ink ejection direction.

  Contrary to the dummy nozzle 16, the discharge nozzle 15 has a shape in which the diameter in the nozzle narrows in the ink discharge direction.

  Further, the dummy nozzle 16 has an opening that opens larger than the opening area of the discharge nozzle 15 on the ink discharge side on the ink discharge side. The diameter Dod at the opening of the dummy nozzle 16 of the present embodiment is set to be substantially the same as the diameter Dir on the inlet side of the discharge nozzle 15. The diameter Did on the inlet side of the dummy nozzle 16 is set to be substantially the same as the diameter Dor on the outlet side of the discharge nozzle 15. The ejection nozzle 15 and the dummy nozzle 16 are formed so that the taper shape is symmetric with respect to the direction in which the ink droplets are ejected.

As a suitable example of the dimensions of the dummy nozzle 16 and the discharge nozzle 15,
The diameter Dod of the ink discharge side of the dummy nozzle 16: 54 μm
Inlet side diameter Did of dummy nozzle 16: 27 μm
Outlet side diameter Dor of discharge nozzle 15: 27 μm
Inlet side diameter Dir of the discharge nozzle 15: 54 μm
Nozzle (dummy nozzle 16, discharge nozzle 15) length Ln: 50 μm
Is mentioned.

  In this case, the ratio of the cross-sectional area on the ink discharge side of the dummy nozzle 16 and the cross-sectional area on the ink discharge side of the discharge nozzle 15 is 4: 1 because it is proportional to the square of the respective apertures. That is, at the position of the ink meniscus m, the flow rate of ink in the dummy nozzle 16 is ¼ of the flow rate of ink in the discharge nozzle 15. Thereby, even when the pressure of the ink in the pressure chambers 7a to 7d becomes high, ink droplets are not ejected from the dummy nozzle 16.

  Further, as in the case of the dummy nozzle 16, when the ink discharge side diameter Dod is larger than the inlet side diameter Did, the force of the ink meniscus m to hold its position is weakened by the surface tension of the ink. The limit Ps of when the surface tension σ of the ink is 30 mN / m,

It is -2222Pa if it calculates using the type | formula of this.

  The ink hydrostatic pressure on the nozzle surface needs to be maintained between 0 and -2222 Pa. Normally, there is no problem because the ink supply pressure is adjusted so that the ink hydrostatic pressure on the nozzle surface is about -1000 Pa.

  Even if the ink hydrostatic pressure instantaneously falls below the negative pressure limit Ps, the nozzle meniscus m decreases as the ink meniscus m moves backward in the dummy nozzle 16, and the negative pressure limit increases. The power to return to position increases.

  For this reason, the ink meniscus m is retracted to the inside of the pressure chamber 7 and bubbles are caught in the inside of the pressure chamber 7, and the limit of the negative pressure that causes the inkjet head 1 to malfunction is the same as that of the discharge nozzle 15.

  The formation of the dummy nozzle 16 and the discharge nozzle 15 as described above can be easily performed by processing using the laser beam L. That is, when a laser irradiation apparatus having an imaging optical system is used, the relative position between the laser projection lens and the nozzle plate 14 is varied by an xyz stage, and the dummy nozzle 16 is formed, as shown in FIG. When the stage is adjusted to align the laser focusing surface with the lower surface of the nozzle plate 14 and the discharge nozzle 15 is formed, the laser focusing surface is adjusted to the upper surface of the nozzle plate 14 by adjusting the z stage as shown in FIG. Match.

The acoustic characteristics of the dummy nozzle 16 and the discharge nozzle 15 are as follows. In the discharge nozzle 15 of FIG.
p (t): Ink pressure at nozzle inlet q (t): Ink flow rate at nozzle inlet M: Inertial resistance of ink in nozzle R: Viscosity resistance of ink in nozzle ρ: Ink density y (x): Position x Nozzle radius r (y): pressure gradient due to viscosity per unit flow rate of ink flowing through a cylinder of radius y Ln:
Equation of motion for ink in nozzles

However,

Holds.

  From the equation (2), it can be seen that the acoustic property of the nozzle as viewed from the pressure chamber 7, that is, the fluid impedance, is characterized by the inertial resistance M and the viscous resistance R.

  Here, as shown in FIG. 6, when considering the inertial resistance M ′ and the viscous resistance R ′ of the dummy nozzle 16 facing away from the discharge nozzle 15,

Is obtained.

  According to the equations (5) and (6), the inertial resistances M and M ′ and the viscous resistances R and R ′ of the discharge nozzle 15 and the dummy nozzle 16 having opposite shapes are the same. It can be seen that the fluid impedances are the same.

  Accordingly, when the diameter Dod of the dummy nozzle 16 is substantially the same as the inlet diameter Dir of the discharge nozzle 15 and the inlet diameter Did of the dummy nozzle 16 is substantially the same as the outlet diameter Dor of the discharge nozzle 15 as in the present embodiment. The dummy nozzle 16 and the discharge nozzle 15 have substantially the same fluid impedance.

  Thereby, the pressure vibration characteristics of the pressure chambers 7b to 7d outside the printing range and the pressure vibration characteristics of the pressure chambers 7e, 7f,... Within the printing range can be made substantially the same, and the pressure chamber 7b, The main acoustic resonance frequencies of the ink in 7c and 7d can be made substantially the same as the main acoustic resonance frequencies of the pressure chambers 7e, 7f, 7g,.

  Further, when ink is sucked from the discharge nozzle 15 and the dummy nozzle 16 during maintenance of the ink jet head 1, in the conventional ink jet head in which a plurality of dummy nozzles are provided in the dummy pressure chamber, more ink than necessary is dummy. Out of the pressure chamber.

  On the other hand, in the present embodiment, the dummy nozzle 16 and the discharge nozzle 15 have the same viscous resistance, so that more ink than necessary does not flow out of the dummy pressure chamber. Thereby, waste of ink during maintenance can be reduced.

  Here, FIG. 7 is a timing chart of the drive signal WW output from the driver IC to the electrode 12 during solid printing. A drive signal is not given to the electrode 12a, and it is a constant potential. The same potential as the electrode 12e is always applied to the electrode 12b. The same potential as that of the electrode 12f is always applied to the electrode 12c. The same potential as that of the electrode 12g is always applied to the electrode 12d. FIG. 7 illustrates only one end side of the inkjet head 1, but the same applies to the other end side of the inkjet head 1.

  The drive signal is time-divided into three phases, and when ink is ejected from a certain nozzle 15, ink is not ejected from the nozzle 15 adjacent to the nozzle 15 that ejects ink, and from the nozzle 15 that is adjacent to the nozzle 15.

  The drive signal WW is a continuous series of seven drop signals W. When such a drive signal WW is applied to the pressure chamber 7, one ink droplet is ejected from the ejection nozzle 15 for one drop signal W. For example, when the number of drop signals W in the drive signal WW is 7, seven ink droplets are continuously ejected from the ejection nozzle 15 in the single drive signal WW. Therefore, in order to change the amount of ink droplets adhering to one pixel, the number of drop signals W in the drive signal WW may be changed. Thus, it is possible to perform eight gradation printing including the case where ink is not ejected.

  As shown in FIG. 8, the drop signal W includes an expansion pulse P1 that expands the volume of the pressure chamber 7, a contraction pulse P2 that contracts the volume of the pressure chamber 7, and a pause time between both pulses. . The width of the expansion pulse P1, the rest time, and the width of the contraction pulse P2 are each 1 AL. Here, AL is a time that is ½ of the main acoustic resonance period of the ink in the pressure chamber 7, and the average value of the pressure of the ink in the pressure chamber 7 changes from positive to negative, or from negative to positive. It is time to reverse. The main acoustic resonance frequency that is the reciprocal of the main acoustic resonance period of the ink in the pressure chamber 7 is also called a Helmholtz resonance frequency. The expansion pulse P1 causes ink to be ejected from the ejection nozzle 15, and the contraction pulse P2 has an action of canceling the pressure vibration generated by the expansion pulse P1.

As described above, according to the present invention, the main acoustic resonance period of the ink in the pressure chamber 7 to which the dummy nozzle 16 is communicated is determined as the main acoustic resonance period of the ink in the pressure chamber 7 to which the discharge nozzle 15 is communicated. Although it can be made to substantially coincide with the acoustic resonance period, strictly speaking, the pressure chamber 7 to which the dummy nozzle 16 communicates and the pressure chamber 7 to which the discharge nozzle 15 communicates are nozzles (dummy nozzle 16, discharge nozzle 15). ) Since the neighboring shapes are different, the main acoustic resonance periods of the two may be slightly different. This difference is hardly a problem when only one drop is discharged. However, when a plurality of ink droplets are continuously ejected as in the present embodiment, the timing of the drive signal W is matched with the main acoustic resonance period of the ink in the pressure chamber 4 to which the ejection nozzle 15 communicates. Better.
In the configuration like this, the electrode 12b and the electrode 12e, the electrode 12c and the electrode 12f, the potentials of the electrode 12d and the electrode 12g is respectively the same, when generated partition wall 8d of the pressure chamber 7e, the 8e shear strain simultaneously The partition walls 8a and 8b of the pressure chamber 7b also generate shear strain. Further, when the partition walls 8e and 8f of the pressure chamber 7f generate shear strain, the partition walls 8b and 8c of the pressure chamber 7c also generate shear strain. Furthermore, when the partition walls 8f and 8g of the pressure chamber 7g generate shear strain, the partition walls 8c and 8d of the pressure chamber 7d also generate shear strain. Since the dummy nozzles 16b, 16c, and 16d communicate with the pressure chambers 7b, 7c, and 7d, no ink is ejected even if the pressure chambers 7b, 7c, and 7d are sheared. However, since the fluid impedances of the dummy nozzle 16 and the discharge nozzle 15 are substantially the same, the pressure chambers 7b, 7c, 7d generate substantially the same pressure vibration as the pressure chambers 7e, 7f, 7g,. For this reason, the magnitude of crosstalk leaking from the pressure chambers 7b, 7c, 7d is substantially the same as the magnitude of crosstalk leaking from the pressure chambers 7e, 7f, 7g,. Therefore, at the time of solid printing, the pressure chambers 7e, 7f, 7g located at the end portion in the printing range are both sides like the other pressure chambers 7h, 7i, 7j,... Located inside the printing range. Will receive the same amount of crosstalk. Thereby, the volume of the ink droplets ejected from the ejection nozzles 15e, 15f, 15g can be made substantially the same as the volume of the ink droplets ejected from the ejection nozzles 15h, 15i, 15j,. Thereby, it is possible to prevent density unevenness and image quality deterioration at the end of the printing range.

  In the above-described embodiment, the discharge nozzle 15 and the dummy nozzle 16 in which the inner peripheral surface of the nozzle is formed in a linear taper have been described as examples. However, as shown in FIG. 9, the discharge nozzle 15A and the dummy nozzle The inner peripheral surface of the nozzle 16A may be formed in a curved taper shape. In this case, the fluid impedances of the discharge nozzle 15A and the dummy nozzle 16A can be made substantially the same by forming the discharge nozzle 15A and the dummy nozzle 16A so that the taper shape is symmetric with respect to the ink discharge direction. As stated.

  As described above, according to the inkjet head 1 of the present embodiment, the plurality of pressure chambers 7 arranged in parallel on the straight line across the partition wall 8 and communicated with the ink supply path 9 respectively, and within the printing range. The discharge nozzle 15 provided in the pressure chambers 7e, 7f,..., The pressure chambers 7b to 7d positioned outside the printing range, and the outside communicate with each other, and the ink discharge side of the discharge nozzle 15 on the ink discharge side. And a dummy nozzle 16 having an opening that is larger than the opening area of the discharge nozzle 15 and having a shape that is set to be substantially the same as the fluid impedance of the discharge nozzle 15, and is located within the printing range. When pressurizing the inside ink, ink droplets are ejected from the ejection nozzle 15 and ink droplets are ejected from the dummy nozzles 16 communicated with the pressure chambers 7b to 7d located outside the printing range. To strange. At the same time, the pressure chambers 7b to 7d located outside the printing range are caused to generate pressure vibrations substantially the same as the pressure chambers 7e, 7f, 7g,. Thus, for example, when driving the pressure chamber 7e located at the end within the printing range, both sides of the pressure chamber 7e are disposed in the same manner as the other pressure chambers 7h, 7k,. By applying crosstalk from the other pressure chambers 7b and 7h located, the volume of ink droplets ejected from the ejection nozzle 15e connected to the pressure chamber 7e located at the end of the printing range is within the printing range. The volume of the ink droplets ejected from the ejection nozzle 15h located inside is substantially the same, and density unevenness during printing and deterioration of image quality can be prevented. The same applies to the driving of the pressure chambers 7f and 7g located at the end portions in the other printing ranges.

  Further, according to the ink jet head 1 of the present embodiment, the discharge nozzle 15 and the dummy nozzle 16 are formed in a symmetrical shape in the ink droplet discharge direction, so that the pressure chamber 7e to which the discharge nozzle 15 communicates. , 7f,... And the fluid impedance of the ink in the pressure chambers 7b to 7d connected to the dummy nozzle 16 can be made substantially the same in practice.

  Next, another embodiment of the present invention will be described with reference to FIGS. Note that the same parts as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 10 is a perspective view showing a part of an ink jet printer according to another embodiment of the present invention. The ink jet printer includes a line ink jet head 20. The line inkjet head 20 includes a plurality of inkjet heads 1 arranged in a line, and a head holding member 21 that holds these inkjet heads 1. As shown in FIG. 11, a plurality of inkjet heads 1 in the head holding member 21 are arranged along the arrangement direction of the discharge nozzles and the dummy nozzles. The ink jet heads 1 of the present embodiment are alternately arranged on both surfaces of the plate-like head holding member 21. Thereby, the printing range in each inkjet head 1 can be arranged without a break along the arrangement direction of the inkjet head 1. In the present embodiment, a position facing the discharge nozzle in each inkjet head 1 is set as a printing position.

  The ink jet printer includes a paper transport belt 23 that transports the recording paper 22 so as to pass through a position facing the ink jet head 1 held by the head holding member 21. The sheet transport belt 23 of the present embodiment has an endless belt shape wound around a pair of rollers 24. A drive mechanism (not shown) such as a motor is connected to at least one of the pair of rollers 24. The paper transport belt 23 is driven by the driving mechanism to rotate at least one roller 24, so that the paper transport belt 23 is rotated by the roller 24 and transports the recording paper 22. Thereby, a moving means for moving each inkjet head 1 and the recording paper 22 relatively so that the recording medium passes through the printing position is realized.

  When transporting the recording paper 22 by the paper transport belt 23, for example, the recording paper 22 is attracted to the paper transport belt 23 by static electricity or air flow, or the end of the recording paper 22 is pressed by a pressing member (not shown), The recording paper 22 is brought into close contact with the paper transport belt 23. Note that a method for bringing the recording paper 22 into close contact with the paper transport belt 23 is a known technique, and thus description thereof is omitted.

  FIG. 12 is a block diagram showing various electric circuits included in an inkjet printer according to another embodiment for carrying out the present invention and the relationship between these electric circuits. The ink jet printer includes an image memory 25 that stores image data to be printed on the recording paper 22. The control circuit 26 reads the image data stored in the image memory 25 in a predetermined order when the recording paper 22 conveyed by the paper conveyance belt 23 passes the position facing the inkjet head 1, and the read image data Is sent to the driver IC 27. The driver IC 27 outputs a drive signal WW having a predetermined shape to the corresponding inkjet head 1 in accordance with the print signal. As a result, similarly to the above, printing is performed according to the number of drop signals W in each drive signal WW. Here, drive control means is realized.

  Thus, according to the ink jet printer of the present embodiment, the ink jet head 1 and the recording medium so that the recording medium 22 passes through the print position facing the ejection nozzle 15 provided in the ink jet head 1 of the above-described embodiment. Since the inkjet head 1 is driven based on a drive signal corresponding to the image data, it is possible to prevent density unevenness and image quality deterioration during printing.

1 is a longitudinal side view showing an inkjet head according to an embodiment for carrying out the present invention. It is the AA sectional view. It is explanatory drawing which shows the mode of the volume change of the pressure chamber by shear distortion, (a) shows the state where the volume of the pressure chamber became large, (b) shows the state where the volume of the pressure chamber became small. It is sectional drawing which shows the shape of a discharge nozzle and a dummy nozzle, (a) shows a dummy nozzle, (b) shows a discharge nozzle. It is explanatory drawing explaining the formation process of a discharge nozzle and a dummy nozzle, (a) shows a dummy nozzle, (b) shows a discharge nozzle. It is explanatory drawing which shows the calculation model of the fluid impedance of a discharge nozzle and a dummy nozzle, (a) shows a dummy nozzle, (b) shows a discharge nozzle. It is a timing chart of the drive waveform output with respect to an electrode. It is explanatory drawing which shows the detail of a drive waveform. It is sectional drawing which shows the modification of a discharge nozzle and a dummy nozzle, (a) shows a dummy nozzle, (b) shows a discharge nozzle. It is a perspective view which shows a part of inkjet printer of another embodiment of this invention. It is explanatory drawing which shows the holding state of the inkjet head in the head holding member with which the inkjet printer of another embodiment of this invention is provided. It is a block diagram which shows the various electric circuits with which the inkjet printer of another embodiment for implementing this invention is provided, and the relationship of these electric circuits. It is a front view which shows the inkjet head of a prior art example.

Explanation of symbols

1 Inkjet head 7 Pressure chamber 8 Partition wall 9 Ink supply path 15 Discharge nozzle 16 Dummy nozzle

Claims (4)

A plurality of pressure chambers arranged in parallel on a straight line across the partition wall and communicated with the ink supply path, respectively;
A discharge nozzle provided in the pressure chamber located within a printing range of the pressure chamber;
Pressurizing means for varying the volume of the pressure chamber in response to a drive signal;
Said respectively communicate with said pressure chamber and the outside, located outside the printable area of the pressure chamber, have a set shape such that the fluid becomes impedance substantially the same before Symbol discharge nozzle and the pressure chamber and dummy nozzles which ink is not ejected in Rukoto opening diameter side is smaller than the opening diameter of the outer side,
Selection is made by supplying to the pressure chamber located in the printing range the drive signal for simultaneously changing the volume of the pressure chamber at intervals of N−1 (N ≧ 1 natural number) to the pressurizing means. to a head driving means for varying the volume of the pressure chamber, N-th upon solid printing, from the pressure chamber located at the end of the print range of the pressure chamber varying the volume simultaneously by the driving signal Head driving means adapted to vary the volume of the pressure chamber located outside the printing range;
An inkjet head comprising: The opening diameter of the pressure chamber side of the discharge nozzle ink jet head according to claim 1 which is set larger than the opening diameter of the outer side.   The inkjet head according to claim 2, wherein the ejection nozzle and the dummy nozzle are formed in a symmetrical shape in the ejection direction of the ink droplets. An inkjet head according to claim 1, 2 or 3,
Moving means for relatively moving the inkjet head and the recording medium so that the recording medium passes through a printing position facing the ejection nozzles of the inkjet head;
Driving means for driving the pressurizing means and the head driving means included in the inkjet head based on a drive signal corresponding to image data; and
An inkjet printer comprising:

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