JP6149863B2 - Ink jet head driving method, ink jet head driving apparatus, and ink jet recording apparatus - Google Patents

Description

  The present invention relates to an ink-jet head driving method, an ink-jet head driving apparatus, and an ink-jet recording apparatus, and more specifically, an ink jet capable of suppressing velocity fluctuations at the time of the next droplet discharge caused by pressure reverberation vibration after droplet discharge. The present invention relates to a head driving method, an inkjet head driving apparatus, and an inkjet recording apparatus.

  The ink jet head applies a predetermined drive signal to pressure applying means formed by a piezoelectric element or the like, and mechanically deforms the pressure applying means to expand or contract the volume of the pressure generating chamber in which ink is stored. Ink is ejected from the nozzle in the form of fine droplets by the pressure change caused thereby. In this way, since the ink jet head ejects droplets from the nozzles by the mechanical deformation operation of the pressure applying means, pressure vibrations that periodically repeat positive pressure and negative pressure remain in the pressure generating chamber even after droplet ejection. Hereinafter, the pressure vibration remaining in the pressure generation chamber is referred to as a reverberation pressure wave.

  Such a reverberant pressure wave gradually attenuates and disappears after droplet discharge, but recently, in order to perform high-speed driving, the driving cycle (the cycle in which a driving signal can be applied to the pressure applying means) tends to be shortened. In other words, the reverberation pressure wave generated by the droplet discharge may not completely disappear and may affect the next driving cycle. For this reason, when ejecting droplets from the same nozzle, there is a problem that fluctuations in droplet velocity may occur due to the reverberation pressure wave.

  The influence of the reverberation pressure wave in the same nozzle (the same pressure generation chamber) is usually set appropriately in the drive cycle, and the condition of the reverberation pressure wave when the drive signal is applied in each drive cycle, that is, the reverberation pressure. By making the condition whether the wave is positive pressure or negative pressure become the same, it can be substantially ignored, and the droplet velocity can be stabilized in each driving cycle.

  For example, FIG. 16A shows the relationship between the drive signal and the pressure generated in the pressure generating chamber when the drive signal is applied to each of the three consecutive drive cycles A1 to A3 in the same nozzle. Here, a drive signal Pa (see FIG. 3A) consisting only of an expansion pulse for expanding the volume of the pressure generating chamber is used. The drive signal is indicated by a solid line, and the pressure is indicated by a broken line.

  The duration of each drive cycle A1 to A3 is 5Tc. As shown in the figure, the pressure in the pressure generating chamber becomes negative due to the application of the drive signal Pa consisting of an expansion pulse, but thereafter, the inversion is repeated every 1 Tc from negative to positive and from positive to negative. Note that Tc, which will be described later in detail, is a time that is ½ of the pressure oscillation cycle generated in the pressure generation chamber. When the drive signal Pa is returned to 0 potential at the timing when the pressure is reversed to a positive pressure after 1 Tc, a high pressure is applied to the ink in the pressure generating chamber, and a droplet is ejected from the nozzle. The reverberation pressure wave generated at this time is also applied to the next drive cycle, and is reversed to a positive pressure at the time when the next drive signal Pa is applied. However, when the drive signal Pa is applied at this timing, the positive reverberation pressure wave is inverted to a negative pressure, and the reverberation pressure wave condition is the same as when the drive signal is applied in the drive cycle A1. Therefore, the speed of the liquid droplets discharged in each of the driving cycles A1 to A3 is stable.

  However, droplet ejection is not always performed in each driving cycle A1 to A3. For example, as shown in FIG. 16B, when the driving cycle A2 is non-ejection, a pause from the application of the driving signal Pa in the previous driving cycle A1 to the application of the driving signal Pa in the next driving cycle A3. The period becomes 10 Tc and becomes longer. For this reason, the conditions of the reverberation pressure wave when the drive signal is applied are not the same in the drive cycles A1 and A3. At the time when the drive signal Pa is applied in the drive cycle A3, the pressure in the pressure generation chamber has turned to a negative pressure, and the negative pressure in the pressure generation chamber is further enhanced by the application of the drive signal Pa formed of an expansion pulse. Strong negative pressure state. As a result, a pressure stronger than usual is applied to the pressure generating chamber due to the fall of the drive signal Pa, and the droplet velocity increases.

  As described above, when a continuous drive cycle in the same nozzle includes a non-ejection drive cycle in which a drive signal is not applied, a droplet is applied when a drive signal is applied in a drive cycle subsequent to the non-ejection drive cycle. There has been a problem that the image quality is deteriorated due to the fluctuation of the velocity, the deviation of the landing position and the fluctuation of the droplet amount.

  In Patent Document 1, the frequency of the drive signal is set to an integer that is an integer of 0.5 times the time in which a pressure wave propagates in the pressure generation chamber plus a reciprocal of 0.5 times. It describes that volume fluctuations are prevented.

  However, since the pressure wave propagation time varies depending on the shape of the pressure generation chamber, simply setting the frequency of the drive signal greatly varies the droplet velocity due to variations in the shape of the pressure generation chamber during head manufacture. , Difficult to implement. Moreover, Patent Document 1 does not mention at all the influence of the reverberation pressure wave when the drive signal is next applied after the drive cycle in which the drive signal is applied, with the non-ejection drive cycle interposed therebetween.

  On the other hand, in Patent Document 2, by applying a dummy pulse that falls simultaneously with the fall of the ejection pulse applied to the adjacent pressure generation chamber that ejects ink to the non-ejection pressure generation chamber that does not eject ink, It is described to reduce crosstalk and reverberant pressure waves.

  Patent Document 3 applies either or both of a preliminary pulse composed of a contraction pulse of 2AL (= 2Tc) or more and a second pulse composed of a contraction pulse of 1AL (= 1Tc) immediately before the ejection pulse. Is described.

JP-A-11-170521 JP 2000-255055 A JP 2010-131988 A

  In the method of Patent Document 2, since the dummy pulse is not applied when the discharge pulse is not applied to the adjacent pressure generation chambers, the application of the next drive signal is performed when none of the adjacent pressure generation chambers is non-discharge. The influence of the reverberation pressure wave at the time cannot be prevented, and the fluctuation of the droplet velocity cannot be suppressed.

  Patent Document 3 is intended to reduce the size of droplets and fine vibrations of the meniscus, and does not suppress droplet velocity fluctuations caused by reverberant pressure waves. In order to prevent the influence of the reverberation pressure wave, it is considered necessary to apply a pulse signal having an appropriate pulse width at an appropriate timing, but it is applied immediately before the ejection pulse as disclosed in Patent Document 3. The pulse signal generated is not sufficient to suppress the fluctuation of the droplet velocity due to the influence of the reverberation pressure wave when the drive signal is applied in the drive period next to the non-ejection drive period which is a problem of the present invention. .

  Therefore, in the present invention, when a drive signal is applied in the drive cycle next to the non-ejection drive cycle, a reverberant pressure wave equivalent to the case where the drive signal is also applied in the non-ejection drive cycle is generated. By doing so, the droplet velocity when the drive signal is applied in the next drive cycle can be stabilized, and the droplet velocity fluctuation can be reduced, the inkjet head drive device, and the inkjet recording It is an object to provide an apparatus.

  Other problems of the present invention will become apparent from the following description.

1. In the pressure applying means of the ink jet head having a pressure applying means that operates by applying a drive signal, a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying means, and a nozzle that communicates with the pressure generating chamber, An inkjet head driving method in which the drive signal is applied at a predetermined drive cycle in accordance with image data, and the volume of the pressure generating chamber is expanded or contracted to eject ink from the pressure generating chamber from the nozzle. ,
The drive signal includes an expansion pulse that expands the volume of the pressure generating chamber and maintains the expanded state for a certain period and then returns to the original volume. The expansion maintaining period of the expansion pulse is 0.8 Tc to 1.2 Tc (Tc Is 1/2 of the pressure oscillation period generated in the pressure generation chamber,
When there is a drive cycle in which ejection is not performed at least immediately before the drive cycle in which ejection is performed, the volume of the pressure generation chamber is increased from 0.8 Tc to 1.2 Tc after the start of the drive cycle in which ejection is not performed. Driving an inkjet head that includes a contraction pulse that contracts and maintains a contracted state for a certain period of time and then returns to the original volume, and that applies an adjustment pulse that does not eject ink and has a contraction maintaining period of 0.8 Tc to 1.2 Tc Method.

  2. 2. The inkjet head according to 1, wherein a drive voltage (Von) of the expansion pulse and a drive voltage (Voff) of the adjustment pulse are | Von | / | Voff | = 1 / 0.3 to 1 / 0.7. Driving method.

  3. 3. The ink jet head according to 1 or 2, wherein, when a plurality of drive cycles in which ejection is not performed continues, the adjustment pulse is applied only in a drive cycle in which ejection is not performed immediately before the drive cycle in which ejection is performed first thereafter. Driving method.

  4). When performing multi-gradation driving in which one pixel is recorded by selectively applying the driving signal to the pressure applying unit within a plurality of continuous driving cycles, the plurality of driving cycles for recording the one pixel is performed. Driving in which ejection is performed when there is a driving cycle in which ejection is not performed and there is a driving cycle in which ejection for recording the next one pixel is performed after the driving cycle in which ejection is not performed. 4. The inkjet head driving method according to 1, 2, or 3, wherein the adjustment pulse is applied in a driving cycle in which ejection is not performed at least immediately before the cycle.

  5. The drive signal includes, following the expansion pulse, a contraction pulse that contracts the volume of the pressure generation chamber and maintains the contracted state for a certain period and then returns to the original volume. The contraction maintaining period of the contraction pulse is 1. 5. The method for driving an ink jet head according to any one of 1 to 4 above, which is 8 Tc to 2.2 Tc.

  6). The drive signal includes a contraction pulse that contracts the volume of the pressure generation chamber after a lapse of 0.8 Tc to 1.2 Tc from the fall of the expansion pulse, and returns to the original volume after maintaining the contracted state for a certain period of time, 5. The method for driving an ink jet head according to any one of 1 to 4, wherein a contraction maintaining period of the contraction pulse is 0.8 Tc to 1.2 Tc.

7). A pressure applying means for generating a driving signal, the pressure applying means operating by applying the driving signal; a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying means; and a nozzle communicating with the pressure generating chamber The pressure applying unit of the ink jet head having the pressure is applied with the driving signal at a predetermined driving period in accordance with image data from the driving signal generating unit, and the volume of the pressure generating chamber is expanded or contracted. An ink jet head drive device for discharging ink in a generation chamber from the nozzle,
The drive signal includes an expansion pulse that expands the volume of the pressure generating chamber and maintains the expanded state for a certain period and then returns to the original volume. The expansion maintaining period of the expansion pulse is 0.8 Tc to 1.2 Tc (Tc Is 1/2 of the pressure oscillation period generated in the pressure generation chamber,
The drive signal generation means, when there is a drive cycle in which ejection is not performed at least immediately before the drive cycle in which ejection is performed, 0.8 Tc to 1.2 Tc after the start of the drive cycle in which ejection is not performed, An adjustment pulse that does not eject ink and includes a contraction pulse that contracts the volume of the pressure generation chamber and maintains the contracted state for a certain period and then returns to the original volume, and the contraction maintaining period is 0.8 Tc to 1.2 Tc. Ink-jet head drive device for applying a pressure.

  8). 8. The inkjet head according to 7, wherein the expansion pulse drive voltage (Von) and the adjustment pulse drive voltage (Voff) are | Von | / | Voff | = 1 / 0.3 to 1 / 0.7. Drive device.

  9. The drive signal generating means applies the adjustment pulse only to a drive cycle in which ejection is not performed immediately before a drive cycle in which ejection is first performed when a drive cycle in which ejection is not performed continues. Or a drive device for an inkjet head according to 8;

  10. The drive signal generating unit records one pixel when performing multi-gradation driving to record one pixel by selectively applying the drive signal to the pressure applying unit within a plurality of continuous drive cycles. When there is a driving cycle in which ejection is not performed within a plurality of driving cycles, and there is a driving cycle in which ejection for recording the next one pixel is performed after the driving cycle in which ejection is not performed 10. The inkjet head drive device according to 7, 8, or 9, wherein the adjustment pulse is applied at least in a drive cycle in which ejection is not performed immediately before the drive cycle in which the ejection is performed.

  11. The drive signal includes, following the expansion pulse, a contraction pulse that contracts the volume of the pressure generation chamber and maintains the contracted state for a certain period and then returns to the original volume. The contraction maintaining period of the contraction pulse is 1. The inkjet head drive device according to any one of 7 to 10, which is 8 Tc to 2.2 Tc.

  12 The drive signal includes a contraction pulse that contracts the volume of the pressure generation chamber after a lapse of 0.8 Tc to 1.2 Tc from the fall of the expansion pulse, and returns to the original volume after maintaining the contracted state for a certain period of time, 11. The ink jet head driving apparatus according to any one of 7 to 10, wherein the contraction maintaining period of the contraction pulse is 0.8 Tc to 1.2 Tc.

13. An ink jet head having pressure applying means that operates by applying a drive signal, a pressure generating chamber whose volume expands or contracts by operation of the pressure applying means, and a nozzle that communicates with the pressure generating chamber;
An inkjet recording apparatus comprising: the inkjet head drive device according to any one of 7 to 12 above.

The figure which shows schematic structure of an inkjet recording device 1 shows an example of an inkjet head, (a) is a perspective view showing a part of the inkjet head in cross section, and (b) is a cross sectional view seen from the side. It is a signal waveform diagram showing an example of a drive signal used in the present invention, (a) is a DR waveform, (b) is a DRR waveform, (c) is a DRC waveform. The figure explaining the deformation | transformation operation | movement of the partition by a drive signal Signal waveform diagram showing an example of the adjustment pulse in the present invention The figure which shows the relationship between the drive signal at the time of applying the adjustment pulse in this invention, the adjustment pulse, and the pressure which generate | occur | produces in a pressure generation chamber The figure which shows the relationship between the drive signal and adjustment pulse at the time of using a DRR waveform as a drive signal, and the pressure which generate | occur | produces in a pressure generation chamber. The figure which shows the relationship between the drive signal and adjustment pulse at the time of using a DRC waveform as a drive signal, and the pressure which generate | occur | produces in a pressure generation chamber. The figure which shows the relationship between the drive signal and adjustment pulse at the time of making a drive period different from FIG. 6, and the pressure which generate | occur | produces in a pressure generation chamber. Timing chart illustrating a mode in which adjustment pulses are applied when a plurality of non-ejection drive cycles are continuous Timing chart for explaining another mode of applying an adjustment pulse when a plurality of non-ejection drive cycles are continuous Timing chart explaining a mode of applying an adjustment pulse when performing multi-gradation driving Timing chart for explaining another mode of applying an adjustment pulse when performing multi-tone drive (A) is a timing chart showing a reference example in which a driving signal is applied in all continuous driving cycles, (b) is a timing chart showing an embodiment in which an adjustment pulse is applied in a non-ejection driving cycle, and (c) is 1 Timing chart showing a comparative example in which every other drive cycle is non-ejection FIG. 14 is a graph showing the droplet velocity of the ejected droplets. (A) is a figure which shows the relationship between the drive signal at the time of a drive signal being applied in all the drive cycles, and the pressure which generate | occur | produces in a pressure generation chamber, (b) is a drive signal in case a non-ejection drive cycle is included. Diagram showing the relationship with pressure generated in the pressure generation chamber

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an example of an ink jet recording apparatus according to the present invention.

  In the ink jet recording apparatus 1, the recording medium 100 is sandwiched between the transport roller pair 22 of the transport mechanism 2 and further transported in the Y direction (sub-scanning direction) by the transport roller 21 that is rotationally driven by the transport motor 23. It has become.

  The inkjet head 3 shown in FIG. 2 is provided between the conveyance roller 21 and the conveyance roller pair 22 so as to face the recording surface 101 of the recording medium 100. The inkjet head 3 is mounted on the carriage 5 so that the nozzle surface side faces the recording surface 101 of the recording medium 100, and is electrically connected to the driving device 7 via the FPC 6. The carriage 5 is illustrated along the guide rail 4 that extends across the width direction of the recording medium 100 by a driving unit (not illustrated) that is substantially orthogonal to the conveyance direction (sub-scanning direction) of the recording medium 100. It is provided so as to be able to reciprocate along the 'direction (main scanning direction).

  The inkjet head 3 scans and moves the recording surface 101 of the recording medium 100 in the XX ′ direction as the carriage 5 moves in the main scanning direction, and discharges droplets from the nozzles during the scanning movement. Record the desired inkjet image.

  FIG. 2 shows an example of the ink jet head 3, (a) is a perspective view showing a part of the ink jet head 3 in cross section, and (b) is a cross sectional view seen from the side.

  In the ink jet head 3, reference numeral 30 denotes a channel substrate. A large number of narrow grooves 31 serving as pressure generation chambers and partition walls 32 serving as pressure applying means are arranged side by side on the channel substrate 30 alternately. A cover substrate 33 is provided on the upper surface of the channel substrate 30 so as to block all the channels 31 above. A nozzle plate 34 is bonded to the end surfaces of the channel substrate 30 and the cover substrate 33, and a nozzle surface is formed by the surface of the nozzle plate 34. One end of each channel 31 communicates with the outside through a nozzle 34 a formed on the nozzle plate 34.

  The other end of each channel 31 gradually becomes a shallow groove with respect to the channel substrate 30, and communicates with a common flow path 33 a common to each channel 31 formed in the cover substrate 33. The common flow path 33 a is further closed by a plate 35, and ink is supplied from the ink supply pipe 35 b into the common flow path 33 a and each channel 31 through an ink supply port 35 a formed in the plate 35.

  Each partition wall 32 is made of a piezoelectric element such as PZT which is an electrical / mechanical conversion means. Here, the upper wall portion 32a and the lower wall portion 32b are both formed by a piezoelectric element that is polarized, and the polarization directions (indicated by arrows in FIG. 2B) are determined by the upper wall portion 32a and the lower wall portion 32b. Although the directions opposite to each other are illustrated, the portion formed by the polarized piezoelectric element may be, for example, only the portion indicated by reference numeral 32 a, and may be at least part of the partition wall 32. The partition walls 32 are arranged in parallel with the channels 31. Accordingly, one partition 32 is shared by the adjacent channels 31 and 31.

  In each channel 31, drive electrodes 36 (see FIG. 4) are formed from the wall surfaces of both partition walls 32 to the bottom surface of the channel 31. When a drive signal of a predetermined voltage is applied to the drive electrode 36 from a drive signal generator 71 which is a drive signal generator provided in the drive device 7, the partition wall 32 is formed between the upper wall portion 32a and the lower wall portion 32b. Shear deformation in the shape of a letter with the joint surface as the boundary. Due to the deformation of the partition wall 32, a pressure wave is generated in the channel 31, and pressure for ejecting from the nozzle 34a is applied to the ink in the channel 31.

  As shown in FIG. 4, the drive device 7 includes a drive signal generator 71 that generates a drive signal to be applied to the drive electrode 36 in each channel 31. 3A to 3C show examples of the drive signal Pa given from the drive signal generator 71 to the drive electrode 36 of the ink jet head 3 at the time of droplet discharge. The operation of the partition wall 32 when each drive signal Pa is applied will be described with reference to FIG.

  The drive signal Pa shown in FIG. 3A is composed only of an expansion pulse composed of a rectangular wave that expands the volume of the channel 31 and maintains the expanded state for a certain period and then returns to the original volume.

  The drive signal Pa is applied from the drive signal generator 71 to the drive electrode 36B of the central channel 31B in which the partition wall 32 shown in FIG. 4A is in a neutral state, and the drive electrodes 36A of the adjacent channels 31A and 31C are both. 36C is grounded, as shown in FIG. 4B, an electric field in a direction perpendicular to the polarization direction (indicated by arrows in the figure) of the piezoelectric elements forming the partition walls 32B and 32C on both sides of the channel 31B is generated. As a result, both the partition walls 32B and 32C are shear-deformed into a U-shape toward each other to expand the volume of the channel 31B. Due to the deformation of the partition walls 32B and 32C, the ink flows into the channel 31B from the common flow path 33a. When this expanded state is maintained by W1 and then returned to 0 potential, the partition walls 32B and 32C return to the neutral state in FIG. As a result, high pressure is applied to the ink in the channel 31B, and droplets are ejected from the nozzle 34a. Hereinafter, the drive signal Pa shown in FIG. 3A is referred to as a DR waveform.

  Thus, the pressure in the channel 31 generated by the deformation toward the outside of the partition wall 32 is repeatedly reversed every 1 Tc from negative to positive and from positive to negative. For this reason, in order to eject droplets efficiently, the expansion maintaining period W1 of the expansion pulse of the drive signal Pa is preferably in the vicinity of 1 Tc where the pressure in the channel 31 changes from negative to positive. The range is 8 Tc to 1.2 Tc.

  Here, Tc refers to a time that is ½ of the pressure oscillation period generated in the channel 31 that is the pressure generating chamber. Tc is measured when the velocity of a droplet ejected when a rectangular wave drive signal is applied to the drive electrode 36, and when the rectangular wave pulse width is changed while the rectangular wave voltage value is kept constant. It is determined as the pulse width that maximizes the drop velocity.

  A pulse is a rectangular wave having a constant voltage peak value. When 0V is 0% and a peak voltage is 100%, the pulse width is 10% of the voltage from 0V and the peak voltage. It is defined as the time between 10% of the falling edge.

  Furthermore, a rectangular wave refers to a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within 1/2, preferably within 1/4 of Tc.

  The drive signal Pa shown in FIG. 3 (b) is composed of a rectangular wave that generates a positive pressure by contracting the volume of the channel 31 for a certain period and then restoring it after the expansion pulse in the expansion maintaining period W1. Has a contraction pulse. The contraction continuation period W2 of the contraction pulse is preferably 1.8 Tc to 2.2 Tc from the viewpoint of efficiently ejecting the droplets.

  The drive signal Pa is applied from the drive signal generator 71 to the drive electrode 36B of the central channel 31B in which the partition wall 32 shown in FIG. 4A is in a neutral state, and the drive electrodes 36A of the adjacent channels 31A and 31C are both. 36C is grounded, as in the case of the DR waveform, due to the expansion pulse, both the partition walls 32B and 32C are shear-deformed outwardly toward each other as shown in FIG. Inflate the volume. Due to the deformation of the partition walls 32B and 32C, the ink flows into the channel 31B from the common flow path 33a. After this expanded state is maintained by W1, a contraction pulse is subsequently applied to the drive electrode 36B of the central channel 31B. Then, as shown in FIG. 4C, both the partition walls 32B and 32C are sheared and deformed in a U-shape toward the inside, and the volume of the channel 31B is contracted. At this time, a higher pressure is applied to the ink in the channel 31B, and a droplet is ejected from the nozzle 34a. After the contraction pulse is maintained by W2, the partition walls 32B and 32C return to the neutral state shown in FIG. Hereinafter, the drive signal Pa shown in FIG. 3B is referred to as a DRR waveform.

  The drive signal Pa shown in FIG. 3 (c) is obtained by restoring the original volume after contracting the volume of the channel 31 for a certain period after the expansion pulse of the expansion maintenance period W1 and then through the rest period (zero potential period) W3. It has a contraction pulse consisting of a square wave that generates a positive pressure. Similarly, from the viewpoint of efficiently ejecting droplets, it is preferable that the duration of the rest period W3 is 0.8 Tc to 1.2 Tc, and the contraction duration W4 of the contraction pulse is 0.8 Tc to 1.2 Tc.

  When this drive signal Pa is applied from the drive signal generator 71 to the drive electrode 36B of the central channel 31B in which the partition wall 32 shown in FIG. 4A is in a neutral state, as in the case of the DR waveform, the expansion pulse As a result, as shown in FIG. 4B, both the partition walls 32B and 32C are sheared and deformed in a U-shape toward each other to expand the volume of the channel 31B. Due to the deformation of the partition walls 32B and 32C, the ink flows into the channel 31B from the common flow path 33a. When the expanded state is maintained at 0.8 Tc to 1.2 Tc and then returned to 0 potential, the partition walls 32B and 32C return to the neutral state, and pressure is applied to the ink in the channel 31B, so that the droplets are ejected from the nozzle 34a. Discharged. After the neutral state is maintained between 0.8 Tc and 1.2 Tc, when a contraction pulse is applied to the drive electrode 36B of the central channel 31B, as shown in FIG. 4C, both the partition walls 32B and 32C are mutually connected. Shear-deformed inwardly toward the inside to shrink the volume of the channel 31B. This cancels the pressure wave remaining in the channel 31B. However, the pressure wave remaining in the channel 31 is not completely canceled by the contraction pulse, and may slightly affect the next driving cycle as a reverberant pressure wave. Hereinafter, the drive signal Pa shown in FIG. 3C is referred to as a DRC waveform.

  The expansion pulse drive voltage (Von) and the contraction pulse drive voltage (Voff) in each drive signal Pa described above are preferably | Von |> | Voff | from the viewpoint of efficiently ejecting droplets.

  Next, a method for applying a drive signal from the drive signal generator 71 to the inkjet head 3 in order to reduce the influence of the reverberation pressure wave in the channel 31 that has ejected the droplet after the droplet has been ejected will be described.

  FIG. 5 shows the adjustment pulse Pb used for reducing the influence of the reverberation pressure wave in the present invention. The adjustment pulse Pb is a rectangular wave contraction pulse that contracts the volume of the channel 31 and maintains the contracted state for a certain period, and then returns to the original volume, but does not eject ink (ink droplets). The contraction maintaining period W5 is set to 0.8 Tc to 1.2 Tc.

  FIG. 6 shows a non-ejection drive among the cases in which the DR waveform is used to perform ejection, non-ejection, and ejection in three consecutive driving cycles A1 to A3, respectively, as in FIG. The relationship between the drive signal and the adjustment pulse when the adjustment pulse Pb is applied in the period A2 and the pressure generated in the channel 31 is shown. The driving signal Pa is applied so that the expansion pulse rises simultaneously with the start of the driving periods A1 and A3 for performing ejection.

  Here, the adjustment pulse Pb is applied to the driving cycle A2 in which ejection is not performed immediately before the driving cycle A3 in which ejection is performed, at a timing after a fixed pause period W0 has elapsed from the start of the driving cycle A2. The rest period W0 is set to 0.8 Tc to 1.2 Tc.

  As a result, an adjustment pulse Pb composed of a contraction pulse is applied almost at the same time as when the pressure that has changed to a positive pressure at the start of the non-ejection drive cycle A2 changes to a negative pressure after 1 Tc. Invert. Thereafter, the inversion is repeated from positive to negative and from negative to positive every 1 Tc, and at the start of the driving cycle A3, the driving signal Pa is applied in the state where the pressure is changed to the positive pressure as at the start of the driving cycle A1. Will be. Thereby, the reverberation pressure wave in the channel 31 at the time of applying the drive signal is the same condition in the drive cycles A1 and A3. Therefore, the pressure at the time of droplet discharge by the drive signal Pa is equal to that in the drive cycle A1, and fluctuations in the droplet velocity are suppressed and stabilized.

  The drive voltage (Von) of the expansion pulse of the drive signal Pa and the drive voltage (Voff) of the adjustment pulse Pb are in the range of | Von | / | Voff | = 1 / 0.3 to 1 / 0.7. Thus, it is preferable that the drive voltage of the adjustment pulse Pb is set. Since the reverberation pressure wave that has reached within the non-ejection drive cycle is attenuated, the drive voltage of the adjustment pulse Pb is set to a voltage lower than the drive voltage of the drive signal Pa without causing droplets to be ejected. The condition of the reverberation pressure wave when the drive signal is applied in the next drive cycle can be made substantially equal to that when the drive signal is applied in the previous drive cycle.

  In FIG. 6, the DR waveform shown in FIG. 3A is used as the drive signal Pa. However, the adjustment pulse Pb functions similarly even when another drive signal is used as the drive signal Pa.

  FIG. 7 shows an example using the DRR waveform shown in FIG. 3B as the drive signal Pa. The driving cycle A = 5 Tc, which is the same as the example of FIG. The driving signal Pa is applied so that the expansion pulse rises simultaneously with the start of the driving periods A1 and A3 for performing ejection.

  As shown in FIG. 7A, when the drive signal Pa is applied to each of the drive periods A1 to A3, the conditions of the reverberation pressure wave at the time of applying each drive signal are the same. Further, as shown in FIG. 7B, the adjustment pulse Pb is applied after the rest period W0 of 0.8 Tc to 1.2 Tc has elapsed from the start of the driving period A2 even when only the driving period A2 is non-ejection. Then, the condition of the reverberation pressure wave when the drive signal is applied in the next drive cycle A3 can be made equal to that when the drive signal is applied in the drive cycle A1. As a result, the pressure at the time of droplet discharge by the drive signal Pa is equal to that in the drive cycle A1, and fluctuations in the droplet velocity in the drive cycle A3 are suppressed and stabilized.

  FIG. 8 shows an example using the DRC waveform shown in FIG. 3C as the drive signal Pa. The driving cycle A = 5 Tc, which is the same as the example of FIG. The driving signal Pa is applied so that the expansion pulse rises simultaneously with the start of the driving periods A1 and A3 for performing ejection.

  As shown in FIG. 8A, when the drive signal Pa is applied to each of the drive periods A1 to A3, the conditions of the reverberation pressure wave when applying each drive signal are the same. Further, as shown in FIG. 8B, the adjustment pulse Pb is applied after a rest period W0 of 0.8 Tc to 1.2 Tc has elapsed from the start of the driving cycle A2 even when only the driving cycle A2 is non-ejection. Then, the condition of the reverberation pressure wave when the drive signal is applied in the next drive cycle A3 can be made equal to that when the drive signal is applied in the drive cycle A1. As a result, the pressure at the time of droplet discharge by the drive signal Pa is equal to that in the drive cycle A1, and fluctuations in the droplet velocity in the drive cycle A3 are suppressed and stabilized.

  In the above description, the driving cycle A is 5 Tc. However, even if the driving cycle changes variously, 0.8 Tc to 1 from the start of the non-ejection driving cycle immediately before the driving cycle in which ejection is performed. By applying the adjustment pulse Pb after .2Tc, the conditions of the reverberation pressure wave when the drive signal is applied can be made equal.

  FIG. 9 shows a case where the driving cycle A = 6 Tc. (A) shows a case where each of the driving cycles A1 to A3 discharges a droplet, and (b) shows a case where only the driving cycle A2 is not discharged. Thus, even if the drive cycle is 6 Tc, the conditions of the reverberation pressure wave at the time of applying each drive signal are the same as long as the drive signal Pa is applied to each drive cycle A1 to A3. When the driving cycle A2 is non-ejection, the adjustment pulse Pb is applied after the rest period W0 of 0.8 Tc to 1.2 Tc has elapsed from the start of the driving cycle A2, thereby driving in the next driving cycle A3. The condition of the reverberation pressure wave at the time of applying the signal can be made equal to that at the time of applying the driving signal in the driving period A1. As a result, the fluctuation of the droplet velocity in the driving cycle A3 is suppressed and stabilized.

  FIG. 10 shows a timing chart when a plurality of non-ejection drive cycles are continuous. Here, the DRR waveform shown in FIG. 3B is used. Here, the adjustment pulse Pb is applied to all the non-ejection driving cycles A3 to A6, respectively. Thereby, it is possible to suppress and stabilize the droplet velocity fluctuation at the time of droplet ejection in the driving cycle A7 to which the driving signal Pa is applied next.

  When the adjustment pulse Pb is applied to each of the plurality of continuous non-ejection drive cycles A3 to A6 as described above, the application timing of each adjustment pulse Pb is 0.8 Tc to the start of each drive cycle A3 to A6. Although it is after 1.2 Tc, it is preferable to set the same application timing within the range of 0.8 Tc to 1.2 Tc from the viewpoint of effectively suppressing fluctuations in the droplet velocity.

  In addition, when a plurality of non-ejection drive cycles are continuous in this way, it is not always necessary to apply the adjustment pulse Pb to all the drive cycles A3 to A6. As shown in FIG. The adjustment pulse Pb may be applied only to the non-ejection drive cycle A6 immediately before the drive cycle A7 in which ejection is first performed after A3 to A6. As a result, the number of adjustment pulses Pb applied can be suppressed, so that power consumption can be reduced accordingly, and heat generation of the inkjet head 3 can also be suppressed.

  The ink-jet head 3 may perform multi-tone driving for recording one pixel by selectively applying the driving signal Pa within a plurality of continuous driving cycles. For example, FIG. 12 shows an example in which one pixel cycle is formed by four consecutive drive cycles A1 to A4. In this case, it is possible to perform five gradation recording from recording one pixel with all driving periods A1 to A4 being non-ejection to ejecting one pixel with all driving periods A1 to A4. it can.

  In FIG. 12, the drive signal Pa is applied only to the first drive cycle A1 in the first pixel cycle Aa, and the drive signal Pa is applied only to the first and second drive cycles A1 and A2 in the next pixel cycle Ab. ing. At this time, the adjustment pulse Pb can be applied to each of the driving cycles A2 to A4 that are non-ejection in the pixel cycle Aa and each of the driving cycles A3 and A4 that are non-ejection in the pixel cycle Aa.

  Further, since the drive cycle A1 for performing ejection in the pixel cycle Ab follows the last non-ejection drive cycle A4 in the first pixel cycle Aa, as shown in FIG. 13, the first drive cycle in the pixel cycle Ab is performed. The adjustment pulse Pb may be applied only to the non-ejection drive cycle A4 immediately before A1. As a result, similarly to the case of FIG. 11, the number of adjustment pulses Pb applied can be suppressed, power consumption can be reduced accordingly, and heat generation of the inkjet head 3 can also be suppressed.

  In the above description, the ink jet head 3 of the type in which the partition wall 32 between the adjacent channels 31 is deformed and driven as the pressure applying means is exemplified as the ink jet head. In such an ink jet head 3, the partition wall 32 for expanding or contracting the volume of the channel 31 is shared by the adjacent channels 31, and the deformation operation of the partition wall 32 extends to the adjacent channels 31. It is not possible to discharge at the same time. For this reason, in the present invention, when such an ink jet head 3 is used, in order to prevent the adjustment operation from applying the adjustment pulse, the discharge operation of the adjacent channel is not affected. It is preferable to use an independent drive type ink jet head in which dummy channels that are not used are alternately arranged.

  However, the inkjet head that can be used in the present invention is not limited as long as the volume of the pressure generating chamber expands or contracts by the application of a drive signal, and the ink in the pressure generating chamber can be ejected from the nozzle. However, the present invention is not limited to one that ejects droplets by deforming the partition walls. Therefore, for example, one wall surface of the pressure generating chamber is used as a vibration plate, and a piezoelectric element such as PZT is laminated on the outer surface of the vibration plate, and the vibration plate is vibrated by mechanical displacement of the piezoelectric element by applying a drive signal to generate pressure. An ink jet head that expands or contracts the volume of the chamber may be used.

  Further, the signal waveform of the drive signal is not limited to the above-described DR waveform, DRR waveform, and DRC waveform, and the volume of the pressure generation chamber is expanded or expanded during droplet discharge according to the structure of the pressure generation chamber. Any signal waveform that contracts may be used.

  Further, as described above, the ink jet recording apparatus according to the present invention performs recording by ejecting liquid droplets in the process of scanning and moving the ink jet head 3 in the width direction (main scanning direction) of the recording medium 100. Not limited to this, the inkjet head 3 is constituted by a line-shaped inkjet head fixed across the width direction of the recording medium 100, and droplets are ejected from the nozzles 34a in the process of moving the recording medium 100 along the Y direction in FIG. May be recorded.

  Hereinafter, the effect of the present invention will be illustrated by examples.

(Reference example)
Using the inkjet head shown in FIG. 2, paying attention to one of the channels, as shown in FIG. 14A, a drive signal Pa is applied in each of a plurality of continuous drive periods A1 to A10, and continuously. Droplet discharge was performed. Each driving cycle A = 5 Tc, and the driving signal Pa used the DRR waveform shown in FIG. The expansion maintenance period of the expansion pulse of the DRR waveform was 1 Tc, and the contraction maintenance period of the contraction pulse was 2 Tc.

  The respective droplet velocities at this time were stable at approximately 7 m / s in any of the driving cycles A1 to A10 as shown in FIG.

(Example)
In the same inkjet head as in the reference example, as shown in FIG. 14B, a plurality of continuous drive cycles A1 to A10 are made non-ejection without applying the drive signal Pa every other drive cycle, and non-ejection drive In cycles A2, A4, A6, and A8, after 1 Tc from the start of each drive cycle, an adjustment pulse Pb having a contraction maintenance period of 1 Tc is applied, and the droplet velocity discharged in drive cycles A3, A5, A7, and A9 Was measured.

  As a result, as shown in FIG. 15, the droplet velocity in the driving cycles A3, A5, A7, and A9 is slightly lower than 7 m / s, but all of the droplet velocity is lower than that in the case where the adjustment pulse Pb is not applied. The fluctuation was greatly suppressed.

(Comparative example)
As shown in FIG. 14C, when the adjustment pulse is not applied in each of the drive periods A2, A4, A6, and A8 in which the drive signal Pa is not applied every other drive period and non-ejection is performed, the subsequent drive As shown in FIG. 15, the droplet velocities in the periods A3, A5, A7, and A9 were all 8 to 9 m / s and varied greatly.

  As described above, by applying the adjustment pulse according to the present invention to the non-ejection driving cycle immediately before the ejection cycle in which ejection is performed, droplet ejection with a stable droplet velocity can be performed as in the case of continuous driving. It has become possible.

1: Inkjet head 2: Transport mechanism 21: Transport roller 22: Transport roller pair 23: Transport motor 3: Inkjet head 30: Channel substrate 31: Channel (pressure generation chamber)
32: Partition wall (pressure applying means)
32a: Upper wall part 32b: Lower wall part 33: Cover substrate 33a: Common flow path 34: Nozzle plate 34a: Nozzle 35: Plate 35a: Ink supply port 35b: Ink supply pipe 36: Drive electrode 4: Guide rail 5: Carriage 6: FPC
7: Drive device 71: Drive signal generator (drive signal generator)
Pa: Drive signal Pb: Adjustment pulse

Claims (13)

In the pressure applying means of the ink jet head having a pressure applying means that operates by applying a drive signal, a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying means, and a nozzle that communicates with the pressure generating chamber, An inkjet head driving method in which the drive signal is applied at a predetermined drive cycle in accordance with image data, and the volume of the pressure generating chamber is expanded or contracted to eject ink from the pressure generating chamber from the nozzle. ,
The drive signal includes an expansion pulse that expands the volume of the pressure generating chamber and maintains the expanded state for a certain period and then returns to the original volume. The expansion maintaining period of the expansion pulse is 0.8 Tc to 1.2 Tc (Tc Is 1/2 of the pressure oscillation period generated in the pressure generation chamber,
When there is a drive cycle in which ejection is not performed at least immediately before the drive cycle in which ejection is performed, the volume of the pressure generation chamber is increased from 0.8 Tc to 1.2 Tc after the start of the drive cycle in which ejection is not performed. Driving an inkjet head that includes a contraction pulse that contracts and maintains a contracted state for a certain period of time and then returns to the original volume, and that applies an adjustment pulse that does not eject ink and has a contraction maintaining period of 0.8 Tc to 1.2 Tc Method.   2. The inkjet head according to claim 1, wherein a driving voltage (Von) of the expansion pulse and a driving voltage (Voff) of the adjustment pulse are | Von | / | Voff | = 1 / 0.3 to 1 / 0.7. Driving method.   3. The inkjet according to claim 1, wherein when a plurality of drive cycles in which ejection is not performed continues, the adjustment pulse is applied only in a drive cycle in which ejection is not performed immediately before the drive cycle in which ejection is performed first thereafter. Head drive method.   When performing multi-gradation driving in which one pixel is recorded by selectively applying the driving signal to the pressure applying unit within a plurality of continuous driving cycles, the plurality of driving cycles for recording the one pixel is performed. Driving in which ejection is performed when there is a driving cycle in which ejection is not performed and there is a driving cycle in which ejection for recording the next one pixel is performed after the driving cycle in which ejection is not performed. 4. The ink jet head driving method according to claim 1, wherein the adjustment pulse is applied in a driving cycle in which ejection is not performed at least immediately before the cycle.   The drive signal includes, following the expansion pulse, a contraction pulse that contracts the volume of the pressure generation chamber and maintains the contracted state for a certain period and then returns to the original volume. The contraction maintaining period of the contraction pulse is 1. It is 8Tc-2.2Tc, The drive method of the inkjet head in any one of Claims 1-4.   The drive signal includes a contraction pulse that contracts the volume of the pressure generation chamber after a lapse of 0.8 Tc to 1.2 Tc from the fall of the expansion pulse, and returns to the original volume after maintaining the contracted state for a certain period of time, The method for driving an inkjet head according to claim 1, wherein a contraction maintaining period of the contraction pulse is 0.8 Tc to 1.2 Tc. A pressure applying means for generating a driving signal, the pressure applying means operating by applying the driving signal; a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying means; and a nozzle communicating with the pressure generating chamber The pressure applying unit of the ink jet head having the pressure is applied with the driving signal at a predetermined driving period in accordance with image data from the driving signal generating unit, and the volume of the pressure generating chamber is expanded or contracted. An ink jet head drive device for discharging ink in a generation chamber from the nozzle,
The drive signal includes an expansion pulse that expands the volume of the pressure generating chamber and maintains the expanded state for a certain period and then returns to the original volume. The expansion maintaining period of the expansion pulse is 0.8 Tc to 1.2 Tc (Tc Is 1/2 of the pressure oscillation period generated in the pressure generation chamber,
The drive signal generation means, when there is a drive cycle in which ejection is not performed at least immediately before the drive cycle in which ejection is performed, 0.8 Tc to 1.2 Tc after the start of the drive cycle in which ejection is not performed, An adjustment pulse that does not eject ink and includes a contraction pulse that contracts the volume of the pressure generation chamber and maintains the contracted state for a certain period and then returns to the original volume, and the contraction maintaining period is 0.8 Tc to 1.2 Tc. Ink-jet head drive device for applying a pressure.   The inkjet head according to claim 7, wherein a drive voltage (Von) of the expansion pulse and a drive voltage (Voff) of the adjustment pulse are | Von | / | Voff | = 1 / 0.3 to 1 / 0.7. Drive device.   The drive signal generation means applies the adjustment pulse only in a drive cycle in which ejection is not performed immediately before a drive cycle in which ejection is first performed when a drive cycle in which ejection is not performed continues. 9. An ink jet head drive device according to 7 or 8.   The drive signal generating unit records one pixel when performing multi-gradation driving to record one pixel by selectively applying the drive signal to the pressure applying unit within a plurality of continuous drive cycles. When there is a driving cycle in which ejection is not performed within a plurality of driving cycles, and there is a driving cycle in which ejection for recording the next one pixel is performed after the driving cycle in which ejection is not performed The inkjet head drive device according to claim 7, 8 or 9, wherein the adjustment pulse is applied at least in a drive cycle in which ejection is not performed immediately before the drive cycle in which the ejection is performed.   The drive signal includes, following the expansion pulse, a contraction pulse that contracts the volume of the pressure generation chamber and maintains the contracted state for a certain period and then returns to the original volume. The contraction maintaining period of the contraction pulse is 1. It is 8Tc-2.2Tc, The drive device of the inkjet head in any one of Claims 7-10.   The drive signal includes a contraction pulse that contracts the volume of the pressure generation chamber after a lapse of 0.8 Tc to 1.2 Tc from the fall of the expansion pulse, and returns to the original volume after maintaining the contracted state for a certain period of time, The inkjet head driving device according to claim 7, wherein a contraction maintaining period of the contraction pulse is 0.8 Tc to 1.2 Tc. An ink jet head having pressure applying means that operates by applying a drive signal, a pressure generating chamber whose volume expands or contracts by operation of the pressure applying means, and a nozzle that communicates with the pressure generating chamber;
An ink jet recording apparatus comprising: the ink jet head drive device according to claim 7.

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