JP5304498B2 - Inkjet recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording device which performs stable ejection even in high-speed multi-drop drive and can suppress deviation of landing positions of multi-drops. <P>SOLUTION: In the inkjet recording device, each driving pulse in one printing period comprises an expansion pulse for expanding volume of a pressure chamber and a contraction pulse for contracting volume of the pressure chamber after a prescribed time from the expansion pulse, wherein a time interval between the driving pulses is 0.3 AL (AL is 1/2 of an acoustic resonance period of the pressure chamber) or more and 1.0 AL or less. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an ink jet recording apparatus.

  In a multi-drop driving ink jet recording apparatus, the density of ink dots constituting one pixel can be adjusted by changing the number of ejected ink droplets in one printing cycle, thereby enabling multi-tone printing. (For example, refer to Patent Document 1).

  Patent Document 1 discloses an ink jet recording apparatus that performs multi-drop driving by applying a driving pulse consisting of only an expansion pulse a plurality of times, and it is assumed that high-speed driving is facilitated because the time required for one driving pulse is short. ing.

  Patent Document 1 also discloses a multi-drop driving method in which driving is performed under a condition in which a driving pulse composed of an expansion pulse and a contraction pulse applied after a predetermined time from the expansion pulse is continuously applied without a time interval. Proposed.

JP 2006-256094 A

  However, the method of performing multi-drop driving by applying a driving pulse consisting only of an expansion pulse a plurality of times disclosed in Patent Document 1 is easy for high-speed driving because the time required for one driving pulse is short, but pressure wave oscillation As a result, the stability is greatly reduced. In addition, in order to obtain stability, it is necessary to provide a long pause time during which no driving pulse is applied after ejection of one droplet or after one channel finishes discharging and before the driving pulse is applied to the adjacent channel. As a result, high-speed driving is difficult.

  Similarly, the method of performing multi-drop driving by continuously applying an expansion pulse and a drive pulse comprising a contraction pulse applied after a predetermined time from the expansion pulse without a time interval is also affected by pressure wave vibration. It is difficult to get large and stable injection.

  In the multi-drop driving method of Patent Document 1, ejection becomes unstable in high-speed driving, and there are problems such as deterioration in printing quality due to landing deviation.

  In the multi-drop driving, the ejection becomes unstable due to the pressure vibration of the ink droplet ejected immediately before, and the print quality is deteriorated due to landing deviation or the like. Therefore, it is necessary to control the pressure wave vibration and the fluctuation of the meniscus position to discharge stably. However, it is difficult to completely cancel the pressure wave vibration in high-speed driving in which driving for the next discharge is performed immediately after the discharge.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording apparatus that solves the above-described problems and that can stably emit even in high-speed multi-drop driving and can suppress a deviation in landing positions of multi-drops.

  The object of the present invention is achieved by the invention described below.

1. A printing cycle including a nozzle for ejecting ink droplets, a pressure chamber communicating with the nozzle, a recording head having pressure generating means for changing the volume of the pressure chamber, and a plurality of drive pulses for ejecting ink droplets, respectively Ink-jet recording comprising drive signal generating means for generating a drive signal to be continuously applied therein, and applying the drive signal to operate the pressure generating means to eject ink droplets from the nozzles In the device
Each drive pulse in one printing cycle has an expansion pulse for expanding the volume of the pressure chamber, and a contraction pulse for contracting the volume of the pressure chamber after a predetermined time from the expansion pulse. time interval 0.3AL (AL 1/2 the acoustic resonance period of the pressure chamber) Ri der least 1.0AL less,
The volume of ink droplets ejected by the first drive pulse in the one printing cycle is V1, and the total volume of n ink droplets ejected by n (n is an integer of 2 or more) drive pulses is Vn. when, V1 ≦ (Vn) / n der Rukoto jet recording apparatus characterized.

2. When the drive voltage of the expansion pulse is Von (V) and the drive voltage of the contraction pulse is Voff (V),
2. The ink jet recording apparatus according to 1 above, wherein the drive voltage Von (V) of the expansion pulse in each drive pulse is substantially equal to each other, and the drive voltage Voff (V) of the contraction pulse is substantially equal to each other. .

  3. 3. The ink jet recording apparatus according to 1 or 2, wherein a pulse width of the expansion pulse, the predetermined time, and a pulse width of the contraction pulse are all 1AL.

4 . 4. The ink jet recording apparatus according to any one of 1 to 3 , wherein a speed of each ink droplet ejected by each driving pulse in the one printing cycle is within a range of ± 20%.

5 . When the drive voltage of the expansion pulse is Von (V) and the drive voltage of the contraction pulse is Voff (V),
| Voff | / | Von | <1 in any one of 1 to 4 , wherein the droplet discharge device is described above.

6 . 6. The droplet discharge device according to 5 above, wherein | Voff | / | Von | = 1/2.

7 . 7. The ink jet recording apparatus according to any one of 1 to 6 , wherein each driving pulse is a pulse made of a rectangular wave.

8 . 8. The ink jet recording apparatus according to any one of 1 to 7 , wherein the pressure generating unit is an electrical / mechanical converting unit.

9 . The electro-mechanical converting means, the 8, characterized in that it is formed of piezoelectric material which deforms in shear mode by forming at least a portion of the partition wall between adjacent pressure chambers, and applies a driving pulse The ink jet recording apparatus described.

10 . Each drive pulse expands the volume of the pressure chamber from a predetermined reference state and then returns to the reference state, a predetermined time during which the reference state is maintained, and contracts the volume of the pressure chamber 10. The inkjet recording apparatus according to any one of 1 to 9 , further comprising a contraction pulse that returns to the reference state, and the reference state is maintained between these drive pulses.

  According to the present invention, it is possible to provide an ink jet recording apparatus capable of stable injection even in high-speed multi-drop driving and capable of suppressing a multi-drop landing position shift.

It is a figure which shows schematic structure of an inkjet recording device. It is a figure which shows schematic structure of the shear mode (shear mode) type inkjet recording head which is one aspect | mode of a droplet discharge head, (a) is a perspective view which shows a partial cross section, (b) is provided with the ink supply part. FIG. (A)-(c) is a figure which shows operation | movement of a recording head. It is a figure which shows the drive signal for implement | achieving the inkjet recording device of embodiment which concerns on this invention. (A)-(c) is explanatory drawing of the time division operation | movement of a recording head. It is a timing chart of the drive signal applied to the electrode of the pressure chamber of each set of A, B, and C. It is a timing chart of a drive signal at the time of using only a positive voltage.

  Although the example of embodiment regarding this invention is shown below, the aspect of this invention is not limited to these.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, the electrical / mechanical conversion means uses a shear mode type recording head that forms a partition wall between adjacent pressure chambers, and ejects ink in the pressure chamber by driving the partition wall, and is composed of a rectangular wave. An example in which a drive pulse is applied will be described.

  FIG. 1 is a diagram showing a schematic configuration of an ink jet recording apparatus according to the present invention. In the inkjet recording apparatus 1, the recording medium P is sandwiched between the conveyance roller pair 32 of the conveyance mechanism 3 and further conveyed in the Y direction in the figure by a conveyance roller 31 that is rotationally driven by a conveyance motor 33.

  The recording head 2 is provided between the conveying roller 31 and the conveying roller pair 32 so as to face the recording surface PS of the recording medium P. The recording head 2 is shown substantially orthogonal to the conveyance direction (sub-scanning direction) of the recording medium P by a driving means (not shown) along the guide rail 4 spanning the width direction of the recording medium P. The flexure cable 6 is mounted on a carriage 5 provided so as to be capable of reciprocating along the XX ′ direction (main scanning direction) so that the nozzle surface side faces the recording surface PS of the recording medium P. Is electrically connected to drive signal generation means 100 (see FIG. 3) provided with a circuit for generating a drive signal.

  The recording head 2 records a desired inkjet image by moving the recording surface PS of the recording medium P in the direction XX ′ in the drawing as the carriage 5 moves, and ejecting ink droplets in this moving process. It has become.

  In the figure, reference numeral 7 denotes an ink receiver, and the recording head 2 is provided at a standby position such as a home position during non-recording. When the recording head 2 is in this standby position, a small amount of ink droplets are discarded toward the ink receiver 7. When the recording head 2 has stopped operating for a long time at this standby position, although not shown, the nozzle surface of the recording head 2 is covered by a cap. Reference numeral 8 denotes an ink receiver provided at a position opposite to the ink receiver 7 with the recording medium P in between. When recording in both reciprocating directions, the same operation is performed when switching from forward to backward movement. Accept discarded ink drops.

  2A and 2B are diagrams showing a schematic configuration of a shear mode type recording head which is an embodiment of the recording head, in which FIG. 2A is a perspective view partially showing a cross section, and FIG. 2B is a state in which an ink supply unit is provided. It is sectional drawing. 3A to 3C are diagrams showing the operation.

  2 and 3, 100 is a drive signal generating means, 2 is a recording head, 21 is an ink tube, 22 is a nozzle forming member, 23 is a nozzle, 24 is a cover plate, 25 is an ink supply port, 26 is a substrate, and 27 is a substrate. The partition, L is the length of the pressure chamber, D is the depth of the pressure chamber, and W is the width of the pressure chamber. A pressure chamber 28 is formed by the partition wall 27, the cover plate 24, and the substrate 26.

  FIG. 1B shows a cross-sectional view of the pressure chamber 28 having one nozzle 23. In the recording head 2 operating in the actual shear mode, as shown in FIG. A large number of pressure chambers 28A, 28B, 28C,... Separated by partition walls 27A, 27B, 27C, 27D,.

  One end of the pressure chamber 28 (hereinafter sometimes referred to as a nozzle end) is connected to the nozzle 23 formed on the nozzle forming member 22, and the other end (hereinafter also referred to as a manifold end) is connected to the manifold 77 and ink. The ink tube 21 is connected to an ink tank (not shown) through the supply port 25.

  Further, the pressure chamber 28 is a shallow groove that gradually becomes shallower from the deep groove portion 28a toward the inlet side (right side in FIG. 2) of the deep groove portion 28a on the outlet side (left side in FIG. 2) of the pressure chamber 28. And a groove portion 28b.

  Each of the partition walls 27A, 27B, 27C, 27D... Is composed of partition walls 27a and 27b made of two piezoelectric materials having different polarization directions as indicated by arrows in FIG. Electrodes 29A, 29B, and 29C connected from above the partition wall 27 to the bottom surface of the substrate 26 are formed in close contact with each other, and each electrode 29A, 29B, and 29C generates a drive signal via the anisotropic conductive film 78 and the flexible cable 6. Connected to means 100.

  Each partition 27 is composed of two partition walls 27a and 27b having different polarization directions as indicated by arrows in FIG. 3, but the piezoelectric material may be, for example, only the portion 27a. Of at least some of them.

  The drive signal generation means 100 generates a drive signal generation circuit that generates a series of drive signals for continuously applying a plurality of drive pulses every pixel period (every printing period), and generates the drive signal for each pressure chamber. It consists of a drive pulse selection circuit that selects a drive pulse from the drive signal supplied from the circuit according to the image data of each pixel and supplies it to each pressure chamber, and performs electrical / mechanical conversion according to the image data of each pixel A driving pulse for driving the partition wall 27 as means is supplied. Each drive pulse within one pixel cycle has an expansion pulse that expands the volume of the pressure chamber and a contraction pulse that contracts the volume of the pressure chamber after a predetermined time from the expansion pulse, and the time interval between these drive pulses is It is set to 0.3 AL (AL is 1/2 of the acoustic resonance period of the pressure chamber) or more and 1.0 AL or less.

  The time interval between drive pulses refers to the time interval from the end of application of the immediately preceding drive pulse to the start of application of the next drive pulse. The predetermined time refers to a time interval from the end of application of the expansion pulse to the start of application of the contraction pulse.

  When the image data is received, a control unit (not shown) controls the motor of the conveyance roller and the carriage motor, respectively, and causes the drive signal generation circuit to generate a drive signal having a plurality of drive pulses. Further, the control unit outputs information on the drive pulse to be selected to the drive pulse selection circuit based on the image data. Then, the drive pulse selection circuit selects one or more predetermined drive pulses from the plurality of drive pulses based on the above information and supplies them to the partition wall 27. Thereby, one or more ink droplets can be ejected from the nozzles 23 of the recording head 2 within one pixel period.

  In such a recording head 2, when a drive pulse is applied to the electrodes 29A, 29B, and 29C formed in close contact with the surfaces of the partition walls 27 under the control of the drive signal generating means 100, the operation in the pressure chamber 28 is performed by the operation exemplified below. Ink is ejected from the nozzle 23 as ink droplets. In FIG. 3, the nozzle is omitted.

  When no drive pulse is applied to any of the electrodes 29A, 29B, and 29C, none of the partition walls 27A, 27B, and 27C is deformed, but in the state shown in FIG. 3A, the electrodes 29A and 29C are grounded and the electrodes When an expansion pulse is applied to 29B, an electric field in a direction perpendicular to the polarization direction of the piezoelectric material constituting the partition walls 27B and 27C is generated, and both the partition walls 27B and 27C are deformed at the joint surfaces of the partition walls 27a and 27b, As shown in FIG. 3B, the partition walls 27B and 27C are deformed toward each other, expand the volume of the pressure chamber 28B, generate a negative pressure in the pressure chamber 28B, and ink flows.

  Further, after maintaining this state for a predetermined time, when the potential is returned to 0, the partition walls 27B and 27C return from the expanded position shown in FIG. 3B to the neutral position shown in FIG. High pressure is applied to the ink. As a result, the ink meniscus in the nozzle due to a part of the ink filling the pressure chamber 28B changes in the direction pushed out from the nozzle. When the positive pressure becomes so large that the ink droplet is ejected from the nozzle, the ink droplet is ejected from the nozzle.

  After holding the state returned to the neutral position for a predetermined time, as shown in FIG. 3C, a contraction pulse (cancellation pulse) is applied so as to deform the partition walls 27B and 27C in opposite directions, and the pressure chamber 28B. When the volume is contracted, a positive pressure is generated in the pressure chamber 28B, and a part of the remaining pressure wave is canceled.

  After holding this state for a predetermined time, when the potential is returned to 0 and the partition walls 27B and 27C are returned from the contracted position to the neutral position, a part of the remaining pressure wave is canceled. Each of the other pressure chambers operates in the same manner as described above by applying a drive pulse.

  As described above, ink droplets fly to form an image. In order to form a gradation image or a high-density image in detail, the pressure generating means according to the image data within the same pixel period as described above. A series of drive pulses can be applied multiple times in succession to cause a plurality of ink droplets to fly, thereby forming one pixel (dot) with the plurality of ink droplets. As a result, it is possible to form a high-quality image by enlarging the dots filling the pixels or by forming a plurality of ink droplets on one pixel to form gradation and high density pixels.

  When the plurality of ink droplets are combined to form one pixel, the plurality of individual ink droplets are referred to as sub-drop SD, and the combination is referred to as super drop.

  In order to form a super drop by landing a plurality of sub-drops SD within one pixel, it is basically necessary to reduce variation in the speed at which each sub-drop SD flies. If there is a large variation in the speed at which each sub-drop SD flies, the printing quality will be lowered due to the reduced accuracy of the landing position of the sub-drop SD.

  In multidrop driving, it is necessary to cancel the residual pressure wave for each SD discharge as appropriate. If the residual pressure wave is too large, the speed varies among SDs, and a plurality of SD (ink droplets) forming one pixel lands away from each other, and the pixels are distorted or cannot be stably ejected due to fluctuations in the meniscus position. Occur.

  The driving signal in the present invention is a driving signal for continuously applying a plurality of driving pulses for ejecting ink droplets within one printing cycle, and each driving pulse within one printing cycle is An expansion pulse for expanding the volume and a contraction pulse for contracting the volume of the pressure chamber after a predetermined time from the expansion pulse, and the time interval between these drive pulses is not less than 0.3 AL and not more than 1.0 AL It is characterized by.

  Note that AL (Acoustic Length) is ½ of the acoustic resonance period of the pressure chamber. The pulse width is defined as the time between 10% from the start of voltage rise and 10% from the start of voltage fall. This AL measures the speed of ink droplets ejected by applying a rectangular wave voltage pulse to the partition wall 27 which is an electrical / mechanical conversion means, and changes the pulse width of the rectangular wave while keeping the rectangular wave voltage value constant. The pulse width at which the flying speed of the ink droplet is maximized. Further, the rectangular wave is a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within ½, preferably within ¼ of AL.

  FIG. 4 shows a drive signal applied to the partition wall 27 from the drive signal generation circuit 100 in order to eject ink droplets in the present embodiment. FIG. 4 is a diagram showing a waveform of a drive pulse for forming and flying a super drop in the present embodiment. Time is plotted on the horizontal axis and the voltage of the drive pulse is plotted on the vertical axis.

If in this embodiment, to form the N (N is an integer of 2 or more) sub-drop _SD 1 _of, SD 2, 1 or super drop UD by · · · _{SD N-1,} SD _N, FIG. as shown in 4, sub-drop _{SD 1, SD 2 ··· SD N} -1, the driving pulse _P 1 for ejecting SD _{N respectively,} P 2, drive cycle of the ··· _{P N-1, P N} Even if it is shortened to drive at high speed, the super drop UD can be formed stably as will be apparent from the following description.

4, B ₁ , B ₂ ,... B _N−1 , B _N are pulse widths of the respective expansion pulses, C ₁ , C ₂ ,... C _N−1 , C _N are the respective contraction pulses (cancellation). the pulse width of the _{pulse), K 1, K 2,} ··· K N-1, K N is the time interval between each inflation pulses with decreasing _{pulse, Y 1, Y 2, ···} Y N-1 is the drive pulse , Y _N is the time interval between the last drive pulse and the first drive pulse of the next pixel, t ₁ , t ₂ ,... T _N−1 , t _N are the period of each drive pulse, respectively. Show.

In this embodiment, each drive pulse in one printing cycle includes an expansion pulse for expanding the volume of the pressure chamber, and a contraction pulse (cancellation pulse) for contracting the volume of the pressure chamber after a predetermined time from the expansion pulse. Y ₁ , Y ₂ ,..., Y _N−1 , which are time intervals between the drive pulses, are set to 0.3 AL or more and 1.0 AL or less.

  In this way, the drive pulse is configured as described above, and the time interval between the drive pulses is set to a value between 0.3 AL and 1.0 AL, thereby canceling the residual pressure wave vibration at the time of ejection of each droplet. In addition, since the residual pressure wave vibration is greatly suppressed, the driving cycle for each shot can be shortened, and high-speed driving becomes possible. In addition, since there is little residual vibration, it is possible to emit stably, the variation in the position where each sub-drop reaches the pixel can be suppressed, and the print quality can be improved.

  That is, although the residual pressure wave oscillation at the time of ejection of each droplet is suppressed by the contraction pulse (cancellation pulse), it cannot be suppressed to 0 and a part remains. By setting the time interval between drive pulses to a value between 0.3 AL and 1.0 AL, the pressure wave between this remaining pressure wave and the pressure wave generated at the pulse edge at the start of the application of the next drive pulse It is presumed that the superimposition is suppressed and stable injection can be performed.

  Moreover, it is preferable that the pulse width of each expansion pulse, the pulse width of each contraction pulse, and the time interval between each expansion pulse and each contraction pulse are all set to 1AL.

  Thus, by setting to 1 AL, the effect of canceling the pressure wave vibration can be enhanced, and the SD injection can be further stabilized.

  Further, when the drive voltage of each expansion pulse is Von (V) and the drive voltage of the contraction pulse is Voff (V), it is preferable to set | Voff | / | Von | <1, more preferably | Set Voff | / | Von | = 1/2.

  Thus, by setting | Voff | / | Von | <1, the effect of canceling the pressure wave vibration can be enhanced, and the injection can be further stabilized.

Further, the volume of ink droplets ejected by the first drive pulse in one pixel period is V ₁ , and the total volume of n ink droplets ejected by n (n is an integer of 2 or more) drive pulses is V 1. is _n, it is preferable that _{V 1 ≦ (V n) /} n.

By driving under such a condition as V ₁ ≦ (V _n ) / n, the meniscus of the nozzle opening that is caused to vibrate by the immediately preceding drive pulse is drawn in the direction of the pressure chamber. Since the SD ink ejection is started by the drive pulse, the ejection can be further stabilized.

  With the drive signal shown in FIG. 4, a maximum of N ink droplets can be ejected to perform printing from 0 gradation to N gradation.

For example, when N = 3, 0 drop (0 gradation), 1 drop (1 gradation) of sub-drop SD ₁ ejected by the first drive pulse within one pixel period, SD ₁ and 1 pixel 2 drops (2 gradations) of SD ₂ ejected by the second drive pulse in the cycle, 3 SD ₃ ejected by SD ₁ and SD ₂ and the third (last) drive pulse in one pixel cycle Printing from 0 gradation to 3 gradations is possible for each drop (3 gradations).

Here, when the volume of the sub-drop SD ₁ is V ₁ , the volume of the sub-drop SD ₂ is V ₂ , and the volume of the sub-drop SD ₃ is V ₃ , the above-described V ₁ ≦ (V _n ) / n is satisfied. For this purpose, the following relationship should be satisfied.

V ₁ ≦ (V ₁ + V ₂ ) / 2
V ₁ ≦ (V ₁ + V ₂ + V ₃ ) / 3
Moreover, it is preferable that the speed of each ink droplet ejected by each drive pulse within one pixel period is within a range of ± 20%.

  By driving under such conditions, the variation in speed between the sub-drops is reduced, so that the variation in the position where each sub-drop reaches the pixel can be kept small, and the print quality can be further improved. it can.

Further, 3 it is preferable (to be described later to set the time interval between the first driving pulse _{P 1} of the last driving pulse _{P N} and the next pixel for discharging the sub-drop SD _N is below 1.0AL more 0.3AL In the cycle drive, the last drive pulse of the set driven in the immediately preceding cycle corresponds to the time interval with the first drive pulse of the set driven in the next cycle).

By thus setting the inclusive 0.3AL 1.0AL, last it can increase the effect of canceling the pressure wave vibration by the driving pulse P _N, the stabilization of the one shot th SD injection of the next pixel Can be planned.

  Further, it is preferable that the drive voltage Von of the expansion pulse in each drive pulse in each pixel cycle is substantially equal to each other, and the drive voltage Voff of the contraction pulse is substantially equal to each other. Here, “substantially equal” means that the drive voltage of the expansion pulse (contraction pulse) in each drive pulse is in the range of ± 0.5V. The voltage indicates the maximum voltage of the pulse.

  Thus, by making the drive voltages of the drive pulses substantially equal, the drive circuit can be simplified and the cost can be reduced.

  Note that the reference voltages of the drive pulse voltage Von and the voltage Voff are not necessarily zero. The voltage Von and the voltage Voff are respectively differential voltages from the reference voltage. In the present embodiment, since the reference voltage is set at the GND level, the voltage can be lowered, and the reduction of the driving voltage can suppress the deterioration of the piezoelectric material (PZT) and the driving voltage is low. It is possible to give a large pressure fluctuation in the pressure chamber.

  Further, when the state held at the reference voltage is set as the reference state, each drive pulse expands the volume of the pressure chamber from a predetermined reference state and then returns to the reference state, and the reference state It is preferable that a predetermined time during which the pressure chamber is maintained and a contraction pulse for contracting the volume of the pressure chamber and then returning to the reference state, and the reference state is maintained between these drive pulses. Since the voltage (reference voltage) at the start point and end point of each drive pulse can be made equal, it is not necessary to add an unnecessary signal for returning the voltage when the drive pulse is continuously generated.

  The pressure chamber in the reference state is preferably in a reference volume state that is neither in an expanded state nor a contracted state.

  Each drive pulse is preferably composed of drive pulses having the same waveform. The configuration of the drive signal generation circuit can be simplified. In the present embodiment, a rectangular wave pulse having a rise time and a fall time which are both nearly zero is used. By using a pulse composed of a rectangular wave, the driving efficiency is improved and the setting of the pulse width is facilitated.

  In the share mode type recording head 2, when the side walls 27 </ b> B and 27 </ b> C of the pressure chamber 28 </ b> B that ejects ink droplets are deformed as described above, the adjacent pressure chambers 28 </ b> A and 28 </ b> C are affected. Ink droplets cannot be ejected simultaneously from 28A and 28C. For this reason, normally, among the plurality of pressure chambers 28, the pressure chambers 28 that are separated from each other with one or more pressure chambers 28 in between are generally combined into one set to form two or more sets. The drive control is performed so that the ink discharge operation is sequentially performed in a time division manner for each group. For example, a so-called three-cycle discharge method is performed in which every two pressure chambers 28 are selected and discharged in three phases. However, when an ink droplet is ejected from one pressure chamber, the vibration of the ejected pressure chamber is also transmitted to the adjacent pressure chamber, so that the next ejection can be performed after these vibrations are reduced to some extent. As another channel configuration, a pressure chamber and an air chamber (dummy channel) that does not contain ink, that is, does not emit ink, are provided alternately at least on both sides of the pressure chamber to discharge ink droplets. There is a way to prevent the influence from being transmitted to the adjacent pressure chamber. In this case, each pressure chamber can eject ink droplets at the same timing. The present invention can be applied to any of the above-described methods, but the latter case is particularly preferable because multidrop ink droplets can be ejected more stably.

  Such a 3-cycle discharge operation will be further described with reference to FIG. In the example shown in FIG. 5, it is assumed that the recording head has nine pressure chambers 28 of A1, B1, C1, A2, B2, C2, A3, B3, and C3. As an example, an example in which seven (N = 7) ink droplets are ejected in one pixel cycle will be described. Further, FIG. 6 shows a timing chart of drive signals applied to the electrodes of the pressure chambers 28 in each set of A, B, and C at this time.

For discharging the first sub-drop SD _1, the expansion pulse width is B _1, and then the pulse width is applied a driving pulse P ₁ consisting of decreasing pulse C ₁ after a predetermined time K _1, then at a given time An interval Y ₁ (0.3 AL or more and 1.0 AL or less) is provided.

Next, in order to discharge the sub-drop SD _2, the expansion pulse with a pulse width B _2, then the pulse width is applied a driving pulse P ₂ consisting of decreasing pulse C ₂ after a predetermined time K _2, then at a given time An interval Y ₂ (0.3 AL or more and 1.0 AL or less) is provided.

Similarly, a driving pulse for discharging sub-drops SD ₃ to SD ₇ is applied at a predetermined time interval Y (0.3 AL or more and 1.0 AL or less). Further, the time interval between the last drive pulse P ₇ for discharging the sub-drop of SD ₇ and the first drive pulse P ₁ of the set driven in the next cycle is set to 0.3 AL or more and 1.0 AL or less.

A period for forming a super drop by 7 drops of SD _{1 to} SD ₇ is defined as a pixel period.

When a super drop is formed by the drive pulse shown in FIG. 6 and is caused to fly, the sub-drops SD _{1 to} SD ₇ can be stably ejected at high speed.

At the time of ink discharge, first, a series of driving pulse voltages for discharging the SD ₁ to SD ₇ are applied to the electrodes of the pressure chambers 28 of the A group (A1, A2, A3), and the electrodes of the pressure chambers adjacent to both are grounded. , to eject ink droplets of _SD 1 to SD ₇ from group a of the nozzle.

  Subsequently, the operation is performed in the same manner as described above for each pressure chamber 28 of the B group (B1, B2, B3) and further to each pressure chamber 28 of the C group (C1, C2, C3).

The above is the case of a solid image (full drive), but actually, the number of ink droplets to be ejected among SD ₁ to SD ₇ is changed according to the print data of each pixel.

  In such a shear mode type ink jet recording head, the deformation of the partition wall 27 occurs due to a voltage difference applied to the electrodes provided on both sides of the wall. Therefore, instead of applying a negative voltage to the electrode of the pressure chamber for discharging ink, FIG. As described above, the same operation can be performed by grounding the electrode of the pressure chamber for discharging ink and applying a positive voltage to the electrodes of the pressure chambers on both sides. According to this latter method, the same effect as that obtained when the drive signal shown in FIG. 6 is applied can be obtained, and a circuit configuration can be made only with a positive voltage, which is advantageous in terms of circuit design.

  In the above embodiment, the pressure generating means (partition wall) is constituted by a piezoelectric element. The ink jet recording apparatus of the present invention is preferable because the control of expanding the volume of the pressure chamber can be easily performed when the pressure generating means is constituted by a piezoelectric element.

  In the above embodiment, a rectangular-wave drive pulse having a sufficiently short rise time and fall time as compared with AL is applied to the piezoelectric element. By using the rectangular wave, it is possible to perform driving using the acoustic resonance of the pressure wave more effectively. Compared with the method using a trapezoidal wave, the efficiency of ejecting ink droplets is good, and it is possible to drive with a low driving voltage and to design a driving circuit with a simple digital circuit. In addition, the pulse width can be easily set.

  In the above embodiment, a shear mode type piezoelectric element that deforms in a shear mode by applying an electric field as a pressure generating means is used. The shear mode type piezoelectric element is preferable because a rectangular-wave drive pulse can be used more effectively, the drive voltage is lowered, and more efficient drive is possible.

  In addition, the ink jet recording apparatus of the present invention exhibits a remarkable effect when the pressure generating means is a shear mode type piezoelectric element. This is because the shear mode type piezoelectric element is driven by utilizing the resonance of the pressure wave, so that pressure vibration is likely to remain, and this makes the discharge unstable when performing multi-drop high-speed driving. .

  However, the present invention is not necessarily limited to ejecting ink droplets from the nozzles by driving the partition wall composed of the electro-mechanical conversion means for the volume of the pressure chamber of the recording head. For example, a recording head of a type that ejects ink droplets from nozzles by changing the volume in the pressure chamber by an electromechanical conversion means made of a piezoelectric material provided outside the pressure chamber, and a heater in the pressure chamber are arranged. An ink jet recording apparatus using a recording head of a type in which ink in a pressure chamber is heated using a heater as a heat source and ink droplets are ejected using energy of bubbles generated during heating may be used.

Hereinafter, although the effect of the present invention is illustrated based on an example, the present invention is not limited to these.
<< Image formation and evaluation 1 >>
(Examples 1-8)
Two share mode type recording heads A (nozzle pitch: 180 dpi, number of nozzles: 256, nozzle diameter: 23 μm, AL: 2.5 μs, ink droplet amount: 4 pl) shown in FIG. 2 are prepared, and the nozzle array of each head However, they were pasted so that they were shifted from each other by 1/2 pitch and arranged in a staggered manner. Accordingly, since each of the heads is a 180 dpi head, the nozzle pitch can be shifted by ½, so that it can be used as a 360 dpi recording head, the number of nozzles can be increased, and a high density recording head can be used. It can be.

  Ink was loaded into an ink jet recording apparatus having the structure shown in FIG. 1 equipped with this two-row head (nozzle pitch: 360 dpi, number of nozzles: 512), and discharged under the following conditions.

  Ink: Acrylic ultraviolet curable ink (viscosity 10 cp (measured value at 50 ° C.), surface tension 30 mN / m (measured value at 25 ° C.)).

Three drive pulses P _{1 to} P ₇ for ejecting sub-drops SD ₁ to SD ₇ shown in FIG. 6 from the pressure chambers of each row of this two-row head (nozzle pitch: 360 dpi, number of nozzles: 512) are 1 Based on the drive signal included in each pixel period, it was divided into three groups and three-cycle driving was performed.

  In each drive pulse, the ratio (| Voff | / | Von |) of the drive voltage Von of each expansion pulse and the drive voltage Voff of each contraction pulse was ½.

Further, the pulse width (B _{1 to} B ₇ ) of each expansion pulse is 1AL, the pulse width (C _{1 to} C ₇ ) of each contraction pulse is 1AL, and the time interval (K _{1 to} K ₇₎ between each expansion pulse and each contraction pulse. ) Was set to 1AL.

The time intervals (Y _{1 to} Y ₆ ) between the drive pulses were changed in eight ways as shown in Table 1. Y _{1 to} Y ₆ were set to the same time interval.

In addition, the time interval Y ₇ between the driving pulse P ₇ that discharges the sub-drop of the last SD ₇ of the group driven in the immediately preceding cycle and the first driving pulse P ₁ of the group that is driven in the next cycle is determined by each of the above driving It was set to be the same as the pulse time interval (Y _{1 to} Y ₆ ). That is, for example, in Example 2 of Table _1, Y 1 to Y ₇ are all set to 0.5 .mu.s, in Example _3, Y 1 to Y ₇ are all set to 0.75Myuesu.

When discharging ink, the ink tank was thermally insulated from the head portion and heated at 50 ° C. Further, LEDs (illuminance (light quantity): 100 mW / cm ² (manufactured by Nichia Corporation (special order), peak wavelength: 365 nm)), which are light irradiation means, are installed on both sides (on the carriage) of the recording head 2, and ink is used. The ink was cured by irradiation with ultraviolet rays 0.1 seconds after landing.

  High quality paper was used as the recording medium. During printing, the recording medium was heated from the back side, and the heater temperature was set so that the surface temperature of the recording medium during image recording was 45 ° C. The surface temperature of the recording medium was measured using a non-contact thermometer (IT-530N type, manufactured by Horiba, Ltd.).

Table 1 shows the results obtained by measuring the emission stability and pixel shape at this time by the following method. In all cases, the performance of Δ or higher was regarded as an acceptable level.
[Measurement method of output stability]
Under each driving pulse application condition, the flying speed of the ink droplet was increased by changing the driving potentials Von and Voff, and the flying state was observed. The upper limit of the flight speed at which no bending in the discharge direction or scattering of satellites occurred was defined as the upper limit of the stable emission speed. It was evaluated by the average value of the SD ₁ ~SD _7.
Evaluation criteria for output stability ○: 8.5 m / s ≦ stable output speed upper limit Δ: 8 m / s ≦ stable output speed upper limit <8.5 m / s
X: Stable emission speed upper limit <8 m / s
[Evaluation of pixel shape]
Each drive pulse has a drive voltage Von of each expansion pulse of 16 V, a drive voltage Voff of each contraction pulse of 8 V, and an image formed on high-quality paper, one dot shape by seven ink droplets that are driven into one pixel. Was magnified and observed with a loupe, and the dot shape was evaluated according to the following evaluation criteria.
A: Seven SD (ink droplets) forming one pixel land at almost the same position, and there is almost no dot shape disturbance.
Δ: Seven SD (ink droplets) forming one pixel landed slightly apart from each other, and the dot shape was somewhat disturbed, but this is within the allowable range.
X: Level at which seven SD (ink droplets) forming a pixel landed away from each other, the pixel is disturbed, the dot shape is poor, and is a practical problem.

(Examples 9 to 20)
A recording head B was prepared in the same manner as the recording head A except that the length L of the pressure chamber was increased to AL: 5.0 μs, and the time interval (Y _{1 to} Y ₆ ) of each drive pulse was expressed. Evaluation was conducted in the same manner except that the number of changes was changed to 12 as shown in 1.

From Table 1, in any of the recording heads A and B having different AL values, the ink jet recording apparatus of the present invention that satisfies the condition that the time interval between drive pulses is 0.3 AL or more and 1.0 AL or less is a comparative example that does not satisfy As compared with the inkjet recording apparatus, it was confirmed that the emission stability was good and the pixel shape of one dot formed by the ink droplets SD _{1 to} SD ₇ was excellent.
<< Image formation and evaluation 2 >>
(Examples 21 to 30)
Using the same recording head as in Evaluation 1, the pulse width B (B _{1 to} B ₇ ) of each expansion pulse is fixed at ₁ AL under the same conditions as in Example 5 or Example 15 in Table 1, and each contraction pulse The pulse width C (C _{1 to} C ₇ ) and the time interval K (K _{1 to} K ₇ ) between each expansion pulse and each contraction pulse were evaluated in the same manner except that they were changed as shown in Table 2. The evaluation results are shown in Table 2.

From Table 2, in each of the recording heads A and B having different values of AL, the pulse width B (B _{1 to} B ₇ ) of each expansion pulse, the pulse width C (C _{1 to} C ₇ ) of each contraction pulse, each The ink jet recording apparatuses of Examples 23 and 28 that satisfy the condition that the time interval K (K _{1 to} K ₇ ) between the expansion pulse and each contraction pulse is ₁ AL are not satisfied. Examples 21, 22, 24 to 27, 29. Compared with 30 inkjet recording devices, the emission stability was good, and it was confirmed that the 1-dot pixel shape formed by each of the ink droplets SD _{1 to} SD ₇ was excellent.
<< Image formation and evaluation 3 >>
(Examples 31 to 40)
Using the same recording head as in Evaluation 1, the ratio between the drive voltage Von of each expansion pulse and the drive voltage Voff of each contraction pulse (| Voff | / |) under the same conditions as in Example 5 or 15 in Table 1. Evaluation was performed in the same manner except that Von |) was changed as shown in Table 3. The evaluation results are shown in Table 3.

From Table 3, the ink jet recording apparatuses of Examples 33 and 38 that satisfy the condition that | Voff | / | Von | is 1/2 are not satisfied in any of the recording heads A and B having different AL values. Compared to 31, 32, 34 to 37, 39, and 40 ink jet recording apparatuses, the emission stability is good, and it can be confirmed that the pixel shape of one dot formed by each ink droplet of SD _{1 to} SD ₇ is excellent. It was.

DESCRIPTION OF SYMBOLS 1 Inkjet recording device 2 Recording head 21 Ink tube 22 Nozzle formation member 23 Nozzle 24 Cover plate 25 Ink supply port 26 Substrate 27 Partition 28 Pressure chamber 3 Conveyance mechanism 31 Conveyance roller 32 Conveyance roller pair 33 Conveyance motor 4 Guide rail 5 Carriage 6 Flexi Cable 7, 8 Ink receiver 100 Drive signal generating means P Recording medium PS Recording surface

Claims (10)

A printing cycle including a nozzle for ejecting ink droplets, a pressure chamber communicating with the nozzle, a recording head having pressure generating means for changing the volume of the pressure chamber, and a plurality of drive pulses for ejecting ink droplets, respectively Ink-jet recording comprising drive signal generating means for generating a drive signal to be continuously applied therein, and applying the drive signal to operate the pressure generating means to eject ink droplets from the nozzles In the device
Each drive pulse in one printing cycle has an expansion pulse for expanding the volume of the pressure chamber, and a contraction pulse for contracting the volume of the pressure chamber after a predetermined time from the expansion pulse. time interval 0.3AL (AL 1/2 the acoustic resonance period of the pressure chamber) Ri der least 1.0AL less,
The volume of ink droplets ejected by the first drive pulse in the one printing cycle is V1, and the total volume of n ink droplets ejected by n (n is an integer of 2 or more) drive pulses is Vn. when, V1 ≦ (Vn) / n der Rukoto jet recording apparatus characterized. When the drive voltage of the expansion pulse is Von (V) and the drive voltage of the contraction pulse is Voff (V),
2. The ink jet recording according to claim 1, wherein the drive voltage Von (V) of the expansion pulse in each drive pulse is substantially equal to each other, and the drive voltage Voff (V) of the contraction pulse is substantially equal to each other. apparatus.   3. The ink jet recording apparatus according to claim 1, wherein a pulse width of the expansion pulse, the predetermined time, and a pulse width of the contraction pulse are all 1AL. Speeds of ink droplets ejected by the drive pulse of the one printing cycle is, the ink jet recording apparatus according to any one of claims 1 to 3, characterized in that in the range within 20% ± . When the drive voltage of the expansion pulse is Von (V) and the drive voltage of the contraction pulse is Voff (V),
| Voff | / | Von | <The apparatus according to any one of claims 1 to 4, characterized in that it is 1. 6. The droplet discharge device according to claim 5 , wherein | Voff | / | Von | = 1/2. Each drive pulse jet recording apparatus according to any one of claims 1 to 6, characterized in that a pulse consisting of a square wave. It said pressure generating means, an ink jet recording apparatus according to any one of claims 1 to 7, characterized in that an electro-mechanical converting means. The electro-mechanical converting means according to claim characterized in that it is formed of piezoelectric material which deforms in shear mode by forming at least a portion of the partition wall between adjacent pressure chambers, and applies a driving pulse 8 2. An ink jet recording apparatus according to 1. Each drive pulse expands the volume of the pressure chamber from a predetermined reference state and then returns to the reference state, a predetermined time during which the reference state is maintained, and contracts the volume of the pressure chamber after, and a contraction pulse to return to the reference state, the ink jet recording apparatus according to any one of claims 1 to 9 in between these drive pulses, wherein the reference state is maintained.

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