JP2004262237A - Liquid droplet discharging device and driving method for liquid droplet discharging head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid droplet discharging device having an effect of improving decap characteristics under a low-temperature and low-humidity environment, capable of discharging droplets stably even immediately after slight oscillation of meniscus and capable of discharging droplets stably at high speed by agitating the liquid in a nozzle effectively, and a driving method for a liquid droplet discharging head. <P>SOLUTION: The liquid droplets discharging device has a drive signal generation means which generates a drive signal consisting of two or more drive pulses; a drive pulse selection means which selects a drive pulse according to the data of each pixel; and a head which discharges liquid from a nozzle arranged corresponding to a channel, by changing the volume of a channel based on the selected drive pulse. The drive pulse is a slight oscillation pulse consisting of rectangular waves as a drive pulse for slight oscillation so that the meniscus in a nozzle does not discharge droplets from the nozzle. A slight oscillation pulse which includes at least one rectangular wave with a pulse width of (2n)AL (AL is 1/2 of an acoustic resonance period of a channel; and n is an integer of 1 or more) is included. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a droplet discharge device and a method of driving a droplet discharge head, and more specifically, suppresses a viscosity increase of a liquid in a nozzle by vibrating a meniscus in the nozzle so as not to discharge a droplet from the nozzle. The present invention relates to a droplet discharge device and a method of driving a droplet discharge head.

  2. Description of the Related Art An ink jet recording head for recording an ink jet image is known as a liquid droplet ejection head that ejects liquid droplets from nozzles by changing the volume of a channel.

  The viscosity of the inkjet ink used in the inkjet recording head is usually about 2 to 5 cp (centipoise) at room temperature. However, recently, as the performance of the ink has been improved, the amount of additives and the like has increased, and the ink at room temperature has a high viscosity of 5 to 10 cp. Such a high-viscosity ink can be ejected by slightly increasing the drive voltage of the recording head as long as the ink is ejected at normal temperature and normal humidity. However, in a low-temperature environment, the viscosity increases to 10 cp or more. In a low-humidity environment, the volatilization of the ink component from the meniscus surface is accelerated, so that the viscosity of the ink on the nozzle surface is rapidly increased, and the ejection becomes extremely difficult.

  As described above, it is extremely difficult to stably eject the thickened ink from the recording head under a low-temperature and low-humidity environment. For example, even if the ejection is interrupted for a very short time, the ejection is not normally performed from the first drop when the ejection is restarted, and the image quality is significantly reduced.

Conventionally, as one of the measures to suppress the increase in ink viscosity on the nozzle surface, the ink with increased viscosity on the nozzle surface is stirred with the ink in the channel by vibrating the meniscus in the nozzle so that it does not discharge from the nozzle tip. Patent Literatures 1 and 2 disclose that the ink at the nozzle tip is agitated to reduce the ink viscosity by applying a slight vibration to the nozzle tip in a state where printing is paused. Have been.
JP-A-11-268264 JP-A-2000-94669

  In a low-temperature, low-humidity environment, the viscosity of the ink rises very fast for the above-described reason. Therefore, the ink must be ejected immediately after micro-vibration is applied to the meniscus. In addition, in order to perform stable ejection, it is necessary that the vibration of the meniscus due to the minute vibration stops and the ejection is performed in a state where the meniscus is fixed. The pod flying speed fluctuates, causing a landing error. Further, in order to stir and mix the ink efficiently, it is necessary to vibrate the meniscus greatly. However, when driving at high speed, it is necessary to attenuate the vibration of the meniscus early.

  The method of effectively shaking the ink meniscus and effectively canceling the residual vibration can be explained from acoustic theory as follows.

  By expanding (or contracting) the channel, the pressure wave generated in the channel gradually attenuates while repeating the inversion of the pressure every 1 AL. When the deformation of the channel is restored at the timing when the pressure is inverted after 1AL after the deformation of the channel, the original pressure and the newly generated pressure reinforce each other, causing the ink meniscus to vibrate greatly. Note that AL (Acoustic Length) is １ ／ of the acoustic resonance period of the channel. Therefore, if the time from when the channel is deformed to when it is restored is set to an odd multiple of AL, the meniscus can be vibrated greatly. However, since the residual pressure is not canceled and the vibration of the meniscus remains, discharge cannot be performed immediately.

  On the other hand, if the channel is deformed and the pressure after 2AL is inverted and then the channel is restored at the timing of re-inversion, the original pressure and the newly generated pressure cancel each other, so that the meniscus does not largely vibrate. Therefore, if the time from the deformation of the channel to the restoration of the deformation is set to an even multiple of AL, the residual pressure is canceled, so that the vibration of the meniscus stops and the discharge can be performed immediately. I can't let that happen.

  As can be understood from the above, in order to discharge high-viscosity ink at high speed and stability in a low-temperature and low-humidity environment, the meniscus is largely vibrated and the ink on the nozzle surface is efficiently stirred. It is necessary to solve the conflicting problem of efficiently canceling residual vibration generated by vibration.

  The techniques of Patent Documents 1 and 2 both apply a micro-vibration pulse due to a trapezoidal wave to a nozzle that does not perform ink ejection to apply micro-vibration to a meniscus. For this reason, after the micro-vibration is applied to the meniscus, there is time until the ink is ejected, and during that time, the ink viscosity increases again, and it is difficult to normally eject the ink particularly in a low-temperature and low-humidity environment. There is a problem. Further, the trapezoidal wave has a complicated circuit configuration and lowers the voltage sensitivity, so that the required driving voltage increases and the power consumption increases. Further, if the number of application of the micro-vibration pulse is not increased, a sufficient effect cannot be obtained, resulting in a problem that the printing speed is reduced.

  Therefore, an object of the present invention is to efficiently stir the liquid in the nozzle, so that the decap characteristic is highly improved even in a low-temperature and low-humidity environment, and to stably discharge droplets even immediately after the micro-vibration of the meniscus. It is an object of the present invention to provide a droplet discharge device and a method of driving a droplet discharge head that can perform high-speed and stable discharge.

  Here, the decap characteristic indicates a decrease in initial velocity due to a so-called decap phenomenon in which the liquid thickens due to meniscus drying when the nozzle surface is open.

  The above object is achieved by the following inventions.

  According to the first aspect of the present invention, there is provided a driving signal generating unit for generating a driving signal including a plurality of driving pulses, a driving pulse selecting unit for selecting a driving pulse according to data of each pixel, and a selected driving pulse. A head that discharges droplets from nozzles provided corresponding to the channels by changing the volume of the channels based on the drive signal, wherein the driving signal is a meniscus in the nozzles. Is a micro-vibration pulse composed of a rectangular wave as a driving pulse for causing micro-vibration to such an extent that droplets are not ejected from the nozzle, and having a pulse width of (2n) AL (AL is の of the acoustic resonance period of the channel) , N is an integer of 1 or more).

  The invention according to claim 2 is the droplet discharge device according to claim 1, wherein the micro-vibration pulse includes a rectangular wave having a pulse width of 2AL.

  The invention according to claim 3 is the droplet discharge device according to claim 1, wherein the micro-vibration pulse includes a rectangular wave having a pulse width of 1AL and 2AL.

  The invention according to claim 4 is the droplet discharge device according to claim 1, 2 or 3, wherein the micro-vibration pulse is applied prior to a discharge pulse for discharging a droplet.

  The invention according to claim 5 is the droplet discharge device according to any one of claims 1 to 4, wherein the (2n) AL rectangular wave is applied at least at the end of the micro-vibration pulse. is there.

  The invention according to claim 6 is the droplet discharge device according to claim 5, wherein an ejection pulse is applied after 1AL of the (2n) AL rectangular wave applied last.

  According to a seventh aspect of the present invention, the ejection pulse for ejecting the droplet is formed by a first pulse composed of a rectangular wave which expands the volume of the channel and returns to the original state after 1 AL, and contracts the volume of the channel after a certain period of time. 7. A droplet discharge according to claim 1, wherein a voltage Von of the first pulse is higher than a voltage Voff of the second pulse. Device.

  The invention according to claim 8 is characterized in that the micro-vibration pulse is formed of a rectangular wave that is restored after contracting the volume of the channel, and has the same voltage as the voltage Voff of the second pulse of the ejection pulse. A droplet discharge device according to claim 7, wherein

  According to a ninth aspect of the present invention, there is provided the droplet discharging apparatus according to any one of the first to eighth aspects, wherein a maximum pushing amount of the meniscus by the minute vibration pulse is equal to or smaller than a nozzle radius.

  According to a tenth aspect of the present invention, the head has an electro-mechanical converter for changing the volume of the channel by applying the ejection pulse or the micro-vibration pulse. 2. The droplet discharge device according to 1.

  An eleventh aspect of the present invention is characterized in that the electromechanical conversion means is formed of a piezoelectric material that forms a partition between adjacent channels and deforms in a shear mode when a voltage is applied. Item 11. A droplet discharge device according to Item 10.

  According to a twelfth aspect of the present invention, there is provided the droplet discharging apparatus according to any one of the first to eleventh aspects, wherein the droplet is ink.

  According to a thirteenth aspect of the present invention, a driving signal including a plurality of driving pulses is generated by a driving signal generating means, and a driving pulse is selected by a driving pulse selecting means in accordance with data of each pixel. A method of driving a droplet discharge head that discharges droplets from nozzles provided corresponding to the channels by changing the volume of a channel of the droplet discharge head based on A micro-vibration pulse composed of a rectangular wave is used as a driving pulse for micro-vibrating the meniscus inside the nozzle so as not to eject a droplet from the nozzle, and has a pulse width of (2n) AL (where AL is the acoustic resonance period of the channel).微, n is an integer of 1 or more) including a micro-vibration pulse including at least one rectangular wave, and applying the micro-vibration pulse to the droplet discharge head. And by a method for driving a droplet discharge head, characterized in that for finely vibrating a meniscus in the nozzle so as not to eject droplets from the nozzle.

  The invention according to claim 14 is the method according to claim 13, wherein the micro-vibration pulse includes a rectangular wave having a pulse width of 2AL.

  The invention according to claim 15 is the method for driving a droplet discharge head according to claim 13, wherein the micro-vibration pulse includes a rectangular wave having a pulse width of 1AL and 2AL.

  The invention of claim 16 is the method of driving a droplet discharge head according to claim 13, 14 or 15, wherein the micro-vibration pulse is applied prior to a discharge pulse for discharging a droplet. .

  The invention according to claim 17 is characterized in that the (2n) AL rectangular wave is applied at least at the end of the micro-vibration pulse. It is a driving method.

  The invention according to claim 18 is the method for driving a droplet discharge head according to claim 17, wherein an ejection pulse is applied one AL after the (2n) AL rectangular wave applied last.

  According to a nineteenth aspect of the present invention, the ejection pulse for ejecting the liquid droplet is composed of a first pulse composed of a rectangular wave that expands the volume of the channel and returns to the original state after 1 AL, and a pulse generated by contracting the volume of the channel after a certain period of time. 20. The droplet discharge according to claim 13, wherein a voltage Von of the first pulse is higher than a voltage Voff of the second pulse. This is a method of driving the head.

  The invention according to claim 20 is characterized in that the micro-vibration pulse is a rectangular wave which is restored after contracting the volume of the channel, and has the same voltage as the voltage Voff of the second pulse of the ejection pulse. 20. A method of driving a droplet discharge head according to claim 19.

  The invention according to claim 21 is the method for driving a droplet discharge head according to any one of claims 13 to 20, wherein the maximum pushing amount of the meniscus by the fine vibration pulse is equal to or less than a nozzle radius. .

  The invention according to claim 22 is characterized in that the droplet discharge head has electro-mechanical conversion means for changing the volume of the channel by applying the discharge pulse or the micro-vibration pulse. A method for driving a droplet discharge head according to any one of the above.

  According to a twenty-third aspect of the present invention, the electro-mechanical conversion means is formed of a piezoelectric material that forms a partition between adjacent channels and deforms in a shear mode when a voltage is applied. Item 23 is a method for driving a droplet discharge head according to Item 22.

  The invention according to claim 24 is the method according to any one of claims 13 to 23, wherein the droplet is ink.

  According to the present invention, it is possible to solve the contradictory problem of efficiently stirring the liquid on the nozzle surface by vibrating the meniscus greatly and efficiently canceling the residual vibration generated by the vibration. The ability to efficiently stir liquids has a high effect of improving decap characteristics even in low-temperature and low-humidity environments, and enables stable ejection of droplets even immediately after micro-vibration of the meniscus, enabling high-speed and stable ejection. And a method for driving a droplet discharge head can be provided.

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

  FIG. 1 is a diagram showing a schematic configuration of an ink jet recording apparatus to which a droplet discharge device according to the present invention is applied. In the inkjet recording apparatus 1, the recording medium P is nipped by a pair of transport rollers 32 of the transport mechanism 3, and is further transported in the Y direction in the figure by a transport roller 31 driven to rotate by a transport motor 33.

  The recording head 2 is provided between the conveyance roller 31 and the conveyance roller pair 32 so as to face the recording surface PS of the recording medium P. The recording head 2 is driven by driving means (not shown) along a guide rail 4 extending across the width of the recording medium P, and is substantially perpendicular to the transport direction (sub-scanning direction) of the recording medium P. A flexure cable 6 is mounted on a carriage 5 provided so as to be able to reciprocate in the XX ′ direction (main scanning direction) so that the nozzle surface side is opposed to the recording surface PS of the recording medium P. Is electrically connected to a drive signal generator 100 (see FIG. 3) provided with a circuit for generating a discharge pulse and a micro-vibration pulse described later.

  The recording head 2 moves the recording surface PS of the recording medium P in the XX ′ direction in the figure with the movement of the carriage 5 and discharges ink droplets in the moving process to record a desired inkjet image. It has become.

  In the drawing, reference numeral 7 denotes an ink receiver, and the recording head 2 is provided at a standby position such as a home position when recording is not performed. When the recording head 2 is at the standby position, the ink thickened at the nozzle opening is slightly vibrated to reduce the viscosity, and then a small amount of ink droplets are discarded toward the ink receiver 7. When the recording head 2 has been stopped at this standby position for a long time, the nozzle surface of the recording head 2 is protected by a cap (not shown). Reference numeral 8 denotes an ink receiver provided at a position opposite to the ink receiver 7 with the recording medium P interposed therebetween, and when printing in both reciprocating directions, when switching from forward movement to backward movement, the same as above. Accept discarded ink drops.

  2 and 3 are views showing an example of the recording head 2, FIG. 2 (a) is a schematic perspective view, FIG. 2 (b) is a sectional view, and FIG. 3 is a view showing an operation at the time of ink ejection. In the figure, 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 partition. A channel 28 is formed by the partition wall 27, the cover plate 24, and the substrate 26.

  As shown in FIG. 3, the recording head 2 is separated between the cover plate 24 and the substrate 26 by a plurality of partitions 27A, 27B, 27C made of a piezoelectric material such as PZT, which is an electromechanical conversion means. A shear mode (share mode) type recording head in which a number of channels 28 are arranged in parallel is shown. FIG. 3 shows three (28A, 28B, 28C) which are a part of the multiple channels 28. One end of the channel 28 (hereinafter sometimes referred to as a nozzle end) is connected to a nozzle 23 formed on the nozzle forming member 22, and the other end (hereinafter sometimes referred to as a manifold end) is connected to the ink supply port 25. After that, it is connected to an ink tank (not shown) by an ink tube 21. Electrodes 29A, 29B, and 29C are formed on the surface of the partition wall 27 in each channel 28 and connected to the bottom surface of the substrate 26 from above the partition walls 27, and the electrodes 29A, 29B, and 29C are connected to the drive signal generation unit 100. Connected to

  The drive signal generation unit 100 includes a drive signal generation circuit that generates a series of drive signals including a plurality of drive pulses for each pixel cycle, and a drive signal supplied from the drive signal generation circuit for each channel. A drive pulse selection circuit for selecting a drive pulse in accordance with the data of each pixel and supplying the selected drive pulse to each channel, and forming a drive pulse for driving the partition wall 27 as an electromechanical conversion means in accordance with the data of each pixel. Supply. This drive pulse includes a micro-vibration pulse and a discharge pulse. Here, the drive signal generation circuit corresponds to a drive signal generation unit, and the drive pulse selection circuit corresponds to a drive pulse selection unit.

  Each partition 27 is made of two piezoelectric materials 27a and 27b having different polarization directions as shown by arrows in FIG. 3, but the piezoelectric material may be, for example, only the portion indicated by reference numeral 27a. 27 at least in part.

  When a discharge 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 generation unit 100, ink droplets are discharged from the nozzles 23 by the operation described below. Note that the nozzles are omitted in FIG.

  First, when no ejection pulse is applied to any of the electrodes 29A, 29B, and 29C, none of the partition walls 27A, 27B, and 27C is deformed, but the electrodes 29A and 29C are grounded in the state shown in FIG. When an ejection pulse is applied to the electrode 29B, an electric field is generated in a direction perpendicular to the polarization direction of the piezoelectric material forming the partition walls 27B and 27C, and both the partition walls 27B and 27C cause slip deformation on the joint surfaces of the partition walls 27a and 27b, respectively. As a result, as shown in FIG. 3B, the partition walls 27B and 27C are deformed outward from each other, the volume of the channel 28B is enlarged, a negative pressure is generated in the channel 28B, and ink flows (Draw).

  When the potential is returned to 0 from this state, the partition walls 27B and 27C return from the expanded position shown in FIG. 3B to the neutral position shown in FIG. 3A, and a high pressure is applied to the ink in the channel 28B ( Release). Next, as shown in FIG. 3C, when a discharge pulse is applied so as to deform the partition walls 27B and 27C in the opposite directions to reduce the volume of the channel 28B, a positive pressure is generated in the channel 28B ( Reinforce). This changes the direction in which the ink meniscus in the nozzle is pushed out of the nozzle by a part of the ink filling the channel 28B. When the positive pressure becomes large enough to eject the ink droplet from the nozzle, the ink droplet is ejected from the nozzle. The other channels operate in the same manner as described above by applying the ejection pulse. Such an ejection method is called a DRR driving method, and is a typical driving method of a print head of a share mode type.

  When the recording head 2 having the plurality of channels 28 at least partially separated from each other by the partition wall 27 made of a piezoelectric material is driven, when one of the partition walls performs an ejection operation, an adjacent channel is affected. Therefore, usually, among the plurality of channels 28, the channels 28 that are separated from each other with one or more channels 28 interposed therebetween are grouped into one set, and divided into two or more sets. Drive control is performed such that the ink discharge operation is sequentially performed in a time-division manner for each set. For example, when all the channels 28 are driven to output a solid image, a so-called three-cycle ejection method is employed in which the channels 28 are selected every two channels and ejected in three phases.

  The three-cycle ejection operation will be further described with reference to FIG. In the example shown in FIG. 4, the description will be made on the assumption that the recording head has nine channels 28 of A1, B1, C1, A2, B2, C2, A3, B3, and C3. FIG. 5 shows a timing chart of a pulse waveform applied to each set of channels A, B, and C at this time.

  At the time of ink ejection, first, a voltage is applied to the electrodes of each channel of the set A (A1, A2, A3), and the electrodes of both adjacent channels are grounded. For example, when a discharge pulse of a positive voltage having a width of 1 AL is applied to the channels of the set A, the partition walls of the channels of the set A to be discharged are deformed outward, and a negative pressure is generated in the channels 28. This negative pressure causes ink to flow from the ink tank into the set A channels 28 (Draw).

  If this state is maintained for 1 AL, the pressure reverses to a positive pressure. Therefore, when the electrodes are grounded at this timing, the deformation of the partition walls returns to the original state, and a high pressure is applied to the ink in the channels 28 of the set A (Release). Further, when a negative voltage is applied to the electrodes of each channel of the set A at the same timing, the partition walls are deformed inward, and a higher pressure is applied to the ink (Reinforce), and the ink column is pushed out from the nozzle. After 1 AL, the pressure is reversed and the pressure in the channel 28 becomes negative, and after 1 AL further elapses, the pressure in the channel 28 is reversed and becomes positive. To cancel the remaining pressure wave.

  Subsequently, each channel 28 of group B (B1, B2, B3), and subsequently, each channel 28 of group C (C1, C2, C3) operates in the same manner as described above.

  In addition, AL (Acoustic Length) is の of the acoustic resonance period of the channel as described above. This AL measures the speed of ink droplets ejected by applying a rectangular wave voltage pulse to the partition wall 27, which is an electromechanical converter, and changes the pulse width of the rectangular wave while keeping the voltage value of the rectangular wave constant. Is obtained as the pulse width at which the flying speed of the ink droplet becomes maximum. A pulse is a rectangular wave having a constant voltage peak value. When 0 V is 0% and the peak value voltage is 100%, the pulse width is defined as 10% of the rise from 0 V and the peak value voltage. Is defined as the time between the fall of 10%. Further, the rectangular wave here refers to a waveform in which both the rise time and the fall time between 10% and 90% of the voltage are within 1/2, preferably 1/4 of AL.

  In such a shear mode type ink jet recording head, since the deformation of the partition wall occurs due to a voltage difference applied to the electrodes provided on both sides of the wall, instead of applying a negative voltage to the electrode of the channel for discharging ink, as shown in FIG. Alternatively, the same operation can be performed by grounding the electrode of the channel from which ink is ejected and applying a positive voltage to the electrodes of both adjacent channels. This latter method is a preferred embodiment because it can be driven only by a positive voltage.

  Next, the operation of applying a slight vibration to the meniscus in the print head 2 of the share mode type will be described with reference to FIGS. Here, a description will be given of a case where a three-cycle ejection operation is performed in the same manner as described above. Here, it is assumed that only the positive voltage is used as the drive waveform voltage, and ejection is performed in the order of group A → group B → group C. Further, here, an example will be described in which the drive signal is composed of one type of drive pulse for each of a micro-vibration pulse and a discharge pulse.

  In the present invention, the micro-vibration pulse for micro-vibrating to the extent that the ink droplet is not ejected from the nozzle is generated in the drive signal generation unit 100 shown in FIG. 3 as in the case of applying the ejection pulse. The micro-vibration pulse in the present invention is characterized by comprising a rectangular wave, and including at least one rectangular wave having a pulse width of (2n) AL (n is an integer of 1 or more).

  In the present invention, by using a rectangular wave as the micro-vibration pulse, the efficiency of micro-vibrating the meniscus is higher than the method using a trapezoidal wave, it is possible to vibrate with a low driving voltage, and it is driven by a simple digital circuit. There is an effect that a circuit can be designed.

  For example, in the example shown in FIG. 7, in the image recording area, first, the electrodes of the channel A are grounded, and the electrodes of the channels B and C are applied to the micro-vibration pulse composed of a 1AL width positive voltage rectangular wave. And a micro-vibration pulse consisting of a positive voltage rectangular wave having a 2AL width is applied at 1AL intervals. Thereby, the meniscus in the nozzles of the channel of the group A is subjected to micro-vibration so as to extrude the ink droplets to such an extent that the ink droplets are not ejected from the nozzles. A micro-vibration of half the intensity of the channels of group A is applied.

  Subsequently, a discharge pulse of a positive voltage having a 1 AL width is applied to the channels of the group A, and a discharge pulse of a positive voltage having a width of 2 AL is applied to the channels of the groups B and C, respectively. Ink is ejected from the channel, and pixels are recorded. When performing multi-drop ejection, these two types of pulses are repeated for the number of droplets to be ejected.

  Similarly, when the discharge from the channel A is completed and the discharge is subsequently performed from the channel B, the electrodes of the channel B are grounded and then the electrodes of the channel A and the channel C are applied to the electrodes of the 1AL width, respectively. A positive voltage micro-vibration pulse and a positive voltage micro-vibration pulse with a 2AL width are applied at 1AL intervals to microvibrate the meniscus. Thereafter, a discharge pulse of a positive voltage having a 1 AL width is applied to the electrodes of the channel B, and a discharge pulse of a positive voltage having a width of 2 AL is applied to the electrodes of the channels A and C to discharge from the channel B. Is performed, and the pixel is recorded. The application and ejection of the micro-vibration pulse of the C group of channels are performed in the same manner.

  Next, a case in which none of the channels of group A, group B, and group C performs ejection and minute vibration is applied to the meniscus in the order of group A → group B → group C will be described with reference to FIG.

  As in FIG. 7, first, the electrodes of the channel A are grounded, and the electrodes of the channels B and C are applied with a 1AL width positive vibration pulse and a 2AL width positive vibration pulse at 1AL intervals. In this case, fine vibration is given to the meniscus in the nozzles of the set A channels. Subsequently, when a pulse of a positive voltage having a 2AL width is applied to any of the channels of the group A, group B, and group C, the ink is not ejected because the partition walls are not displaced.

  Next, a method of selecting a driving pulse in each pixel will be described with reference to FIG. The ON waveform and the OFF waveform in FIG. 9 show two types of drive signals generated by the drive signal generation circuit. This drive signal is composed of three types of drive pulses, i.e., a micro-vibration pulse (1) and ejection pulses (2) and (3), and is an example of a drive signal capable of selecting two-drop multi-drop ejection. is there. The ON waveform and the OFF waveform are respectively supplied to the drive pulse selection circuits of each channel, and are selectively supplied to the electrodes of each channel by controlling the pulse selection gate signal according to the print data of each channel. The drive pulse selection circuit supplies an ON waveform to the electrode when the pulse selection gate signal is high, and supplies an OFF waveform to the electrode when the pulse selection gate signal is low. FIG. 9 shows one cycle of each channel drive of the group A, group B, and group C. Hereinafter, the timing of group A channel drive will be described as an example.

  A pulse division signal is applied during a period before the application of the micro-vibration pulse, a period after the application of the micro-vibration pulse to before the application of the ejection pulse, and a period after the application of the ejection pulse. When the print data of the pixel is supplied, the pulse selection gate signal synchronized with the pulse division signal is turned ON accordingly. During the period when the pulse selection gate signal corresponding to the group A channel is ON ((1) and (2) in FIG. 9), the ON waveform of the driving waveform is applied to the electrodes of the group A channel. Since the pulse selection gate signals corresponding to channels C and C are OFF, the OFF waveform is applied to the electrodes of channels B and C, and the partition walls on both sides of channel A are displaced. In the period of (3) in FIG. 9, the pulse waveforms of the group A, group B, and group C channels are OFF because the pulse selection gate signals of group A, group B, and group C are all OFF. When applied, none of the partitions will be displaced.

  The timing of group B and group C channel drive operates similarly.

  As described above, the micro-vibration pulse is always applied to both the print pixel (in the case of FIG. 7) and the non-print pixel (in the case of FIG. 8), thereby effectively increasing the viscosity of the ink near the nozzle opening. Can be suppressed.

  In particular, as shown in FIG. 7, if the micro-vibration pulse is applied to all the print pixels in the image recording area prior to the ejection pulse, the micro-vibration is always applied to the meniscus immediately before each pixel to be printed. Vibration is applied, so that high-quality printing can be performed with stable ink ejection, and during continuous ejection, residual pressure at the time of previous ejection can be canceled by application of a micro-vibration pulse. Therefore, higher quality image recording can be performed.

  Note that “prior to the ejection pulse” refers to a time within a range in which the effect of improving the decap characteristic is seen in the ejection of the ink droplet after the fine vibration.

  When the micro-vibration pulse is applied to all the print pixels in the image recording area in this manner, the maximum pushing amount of the meniscus that micro-vibrates so as not to eject the ink droplet from the nozzle tip is preferably equal to or less than the nozzle radius. . If the pushing amount due to the meniscus minute vibration is large, the meniscus cannot be completely returned by the timing of the next ink ejection, and stable ejection becomes difficult.However, by suppressing the pushing amount of the meniscus to the nozzle radius or less in this case, Stable ejection is possible even immediately after the meniscus minute vibration.

  The maximum pushing amount is a maximum value of the pushing amount of the meniscus from the nozzle tip in one meniscus pushing operation. The pushing amount of the meniscus from the nozzle 23 can be measured by flash synchronization using, for example, a digital microscope “VH-6300” manufactured by KEYENCE. As shown in FIG. 12, the extrusion amount is a value obtained by measuring the amount of protrusion of the meniscus M from the nozzle tip at a substantially central portion of the nozzle 23 in a direction substantially perpendicular to the nozzle forming member 22.

  The opening shape of the nozzle 23 is not limited to a perfect circle, but may be an elliptical shape or the like. That is.

  In the present invention, it is sufficient that at least one rectangular wave having an even AL width, that is, a pulse width of (2n) AL is included in the micro-vibration pulse, but as shown in FIGS. 7 and 8, the pulse width (2n) If the rectangular wave of AL is included at least at the end of the series of micro-vibration pulses, since there is an effect of canceling the residual pressure wave due to the micro-vibration pulse, the discharge is performed immediately after the meniscus is micro-vibrated. This is preferable when high-frequency driving is performed.

  In addition, here, after 1AL after the meniscus is microvibrated greatly by a microvibration pulse having an odd AL width, microvibration is performed again with a microvibration pulse having an even AL width, and the remaining pressure wave is canceled and then discharged. Is large, and stable ejection is possible.

  When a rectangular wave having a pulse width (2n) AL is applied at the end of the micro-vibration pulse, it is preferable to apply the ejection pulse 1 AL after that, as shown in FIG. The reason is that cancellation of the residual pressure wave by the micro-vibration pulse is not always perfect. Therefore, when the discharge pulse is applied 1 AL after the micro-vibration pulse, the residual pressure wave and the pressure wave by the discharge pulse are in opposite phases, and the residual pressure This is because the influence of the wave on the ejection pulse can be minimized.

  In the above example, n = 1 and one micro-vibration pulse having a pulse width of 2AL is included, but n may be an integer of 2 or more. 7 to 9, the micro-vibration pulse includes a rectangular wave having a pulse width of 1AL and 2AL. In this case, however, the meniscus can be efficiently microvibrated in a short time. This is a preferable mode because the meniscus can be finely vibrated in all pixels without significantly lowering the image recording speed during high-frequency driving in which ink is ejected immediately after the meniscus fine vibration in the system. In addition, a micro-vibration pulse including only a rectangular wave having a pulse width of 2AL is a preferable mode particularly when high-speed drawing is achieved because the meniscus can be micro-vibrated for every pixel in the shortest cycle.

  When two or more rectangular waves having a pulse width of (2n) AL are included in the micro-vibration pulse, n may be different from each other, and the micro-vibration pulse may have a pulse width of (2n) AL. When there are two or more micro-vibration pulses including at least one rectangular wave, the meniscus is efficiently micro-vibrated if the interval between the preceding rectangular wave and the subsequent rectangular wave is an integral multiple of AL. It is preferred because it can be.

  In the examples shown in FIGS. 5, 6, 7 and 9, the ejection pulse expands the volume of the channel and contracts the volume of the channel following the first pulse consisting of a square wave that is restored after 1 AL and 2 AL later. The second pulse is composed of a rectangular wave to be restored, and the voltage Von of the first pulse is higher than the voltage Voff of the second pulse. In particular, the voltage ratio between the voltage Von of the first pulse and the voltage Voff of the second pulse is preferably around Von / Voff = 2/1. Setting Von higher than Voff is a preferable mode because it has the effect of promoting the supply of ink into the channel, especially when the viscosity of the liquid to be discharged is high. The micro-vibration pulse is composed of only a rectangular wave which is restored after contracting the volume of the channel, and is set to the same voltage as the voltage Voff of the second pulse of the ejection pulse. This is a preferable mode because the number of power supply voltages in the drive signal generating unit 100 for generating the ejection pulse and the micro-vibration pulse can be reduced to reduce the circuit cost. In addition, by setting the voltage of the micro-vibration pulse to the low Voff voltage, micro-vibration is not applied too strongly, and micro-vibration that does not cause ink droplets to be ejected from the nozzle can be efficiently applied. The ejection pulse is not limited to the one used in the present embodiment, but includes a drive pulse including a pulse for ejecting a droplet by expanding the volume of the channel and returning or contracting the volume of the channel after a certain period of time. Should be fine.

  As described above, the electro-mechanical conversion means in the present invention is not limited to a piezoelectric material that forms a partition between adjacent channels and is deformed in a shear mode by applying an electric field. Any configuration may be used as long as it gives the function of changing the volume of the channel to the head.However, as shown in the present embodiment, when the head is made of a piezoelectric material that deforms in a shear mode, This is preferable because the above-described rectangular wave can be more effectively used, the driving voltage can be reduced, and more efficient driving can be performed.

  Further, in the above description, an application example of an ink jet recording device is shown as a droplet discharge device, and an application example of an ink jet recording head is shown as a droplet discharge head. However, the present invention is not limited to this. In addition, the present invention can be widely applied as a droplet discharging apparatus and a driving method of a droplet discharging head for discharging a liquid in a channel which is easily thickened as a droplet from a nozzle.

(Evaluation of emission stability 1)
Each channel of the share mode type recording head (number of nozzles: 256, nozzle diameter 23 μm) shown in FIG. 2 is divided into three groups as shown in FIG. 4, and the micro-vibration pulses shown in FIGS. Using the discharge pulse and the discharge pulse, driving was performed for 3 cycles under the following conditions. Table 1 shows the results obtained by measuring the emission stability and the decap characteristic improvement effect at this time by the following methods.

Conditional head: AL = 2.0 μs
Ink: water-based ink
(Viscosity 5.5 mPa · s, surface tension 41 mN / m at 25 ° C)
Drive voltage ratio: Von / Voff = 2/1
Driving cycle: 33 μs

Measurement method of emission stability Under each micro-vibration pulse application condition, the flying speed of the ink droplet was increased by changing the potential difference Von and Voff, and the flying state was observed. The upper limit of the flying speed at which the bending of the ejection direction and the scattering of the satellite do not occur is defined as the upper limit of the stable emission speed.

Evaluation criteria of emission stability ：: 8 m / s ≦ stable emission speed upper limit Δ: 6 m / s ≦ stable emission speed upper limit <8 m / s
×: Upper limit of stable emission speed <6 m / s

Measurement method of decap characteristics Under each micro-vibration pulse application condition, the drive voltage is fixed (Von / Voff = 2/1) to the voltage at which the flying speed of the ink droplet at the time of steady driving becomes 6 m / s, and the ejection interval is extended. While the ink was ejected, the change in the initial velocity was measured. It is recognized that the smaller the speed change at that time, the greater the effect of improvement.

  As shown in Table 1, when a micro-vibration pulse consisting of only a rectangular wave whose pulse width is an odd multiple of AL is applied, the output stability is not sufficient, but a rectangular wave whose pulse width is an even multiple of AL is applied. When a micro-vibration pulse including is applied, stable ejection is possible even immediately after micro-vibrating the meniscus.

(Evaluation of decap characteristics)
Each channel of the print head of the share mode type similar to the case of the evaluation 1 of the emission stability was divided into three groups, and three cycles were driven under the following conditions using the micro-vibration pulse and the ejection pulse shown in FIG. The improvement effect of the decap characteristic and the driving voltage in a low temperature and low humidity environment were evaluated.

  The decap characteristic was measured for one arbitrary nozzle using the following method. The results are shown in FIG.

Conditional head: AL = 2.0 μs
Ink: water-based pigment ink
(Viscosity 11 mPa · s, surface tension 34 mN / m at 11 ° C)
Drive voltage ratio: Von / Voff = 2/1
Driving cycle: 33 μs
Environment: 11 ° C, 35% RH

Measurement method of decap characteristic The drive voltage is changed under the condition that the micro-vibration pulse is not applied to the non-printing pixel and the printing pixel and the condition that the micro-vibration pulse is applied to all the pixels as shown in FIGS. 10C and 10F. The flight speed of the twentieth shot was measured (Von / Voff = fixed at 2/1). Table 2 shows the driving voltage (Von) when the flying speed becomes 6 m / s.

  The driving voltage was fixed at a voltage at which the flying speed during steady driving was 6 m / s, and the change in the initial speed when ink was ejected while the ejection interval was widened was measured. It is recognized that the smaller the speed change at that time, the greater the effect of improvement.

  As shown in Examples 3 and 4 in Table 2, it was confirmed that applying a micro-vibration pulse before ejection was effective in preventing the decap phenomenon in a low-temperature and low-humidity environment. Since a micro-vibration pulse is applied to all the pixels, stable droplet formation can be achieved even with a pattern such as ejection only at the inner edge of the image recording area. Further, by vibrating the meniscus finely before ejection, an effect of improving driving efficiency (reducing driving voltage) can be obtained.

(Evaluation of emission stability 2)
Each channel of the print head of the share mode type similar to the case of the evaluation 1 of the emission stability was divided into three groups, and the amount of ink meniscus pushed out from the nozzle when only the micro-vibration pulse in FIG. , Measuring instrument: Measured using a digital microscope manufactured by KEYENCE.

  Table 3 shows the results of the measurement of the emission stability and the decap characteristic improvement effect by the following method using the micro vibration pulse and the ejection pulse shown in FIG.

Conditional head: AL = 2.0 μs
Ink: water-based ink
(Viscosity 5.5 mPa · s, surface tension 41 mN / m at 25 ° C)
Drive voltage: Von = 17.8V, Voff = 8.9V
Driving cycle: 33 μs

Measuring Method of Ejection Stability Under the condition that the flying speed of the ink droplet is fixed (6 m / s) with the ejection driving voltage fixed, the flying state when only the micro-vibration pulse voltage was changed was observed.

Evaluation criteria for emission stability ：: no discharge bending / misfire, meniscus stable △: partial discharge bending / misfire generation ×: discharge bending / misfire generation, meniscus instability

Measurement method of decap characteristic Under each micro-vibration pulse application condition, the ejection drive voltage was fixed to a voltage at which the flying speed of the ink droplet during steady driving was 6 m / s, and only the micro-vibration pulse voltage was changed. The change in the initial velocity when the ink was ejected while the ejection interval was widened was measured. It is recognized that the smaller the speed change at that time, the greater the effect of improvement.

  As shown in Example 5 and Example 6 in Table 3, when the amount of meniscus extruded by the fine vibration pulse is equal to or less than the nozzle radius (11.5 μm), it is understood that the emission stability is good even immediately after the application of the fine vibration pulse. . Therefore, it is possible to always apply a slight vibration to the meniscus even during high-frequency driving.

  In each of Comparative Examples 7 and 8, the meniscus extrusion amount is larger than the nozzle radius. When only the micro-vibration waveform is applied, misfire (erroneous ejection) does not occur even when the maximum pushing amount of the meniscus is about three times the nozzle radius, but when the ejection waveform is applied before and after the micro-vibration waveform In, when the maximum amount of the meniscus extruded exceeds the nozzle radius (measured value in a state where only the micro-vibration waveform is applied), misfire easily occurs. For this reason, in Comparative Example 7, misfire occurred partially in all the nozzles of the recording head, and in Comparative Example 8, misfire occurred entirely.

The figure which shows the schematic structure of an inkjet recording device (A) is an external perspective view showing an example of a recording head, and (b) is a sectional view. 7A to 7C are diagrams showing the operation of the recording head at the time of ink ejection. (A)-(c) is an explanatory view of a time-division operation of the recording head. Timing chart of pulse waveform applied to each set of channels A, B and C Timing chart of pulse waveform when only positive voltage is used Timing chart of pulse waveforms applied to each set of channels A, B, and C during micro meniscus vibration for all print pixels Timing chart of pulse waveforms applied to each set of channels A, B, and C during meniscus micro-vibration for non-printed pixels A timing chart showing an example in which a micro-vibration pulse and an ejection pulse are selectively applied to channels of group A, group B and group C (A)-(f) is a figure which shows the pulse waveform of a micro-vibration pulse and a discharge pulse, respectively. Graph showing measurement results of decap characteristics Diagram for explaining the amount of meniscus pushed out from the nozzle tip

Explanation of reference numerals

1: inkjet recording apparatus 2: recording head 21: ink tube 22: nozzle forming member 23: nozzle 24: cover plate 25: ink supply port 26: substrate 27: partition wall 28: channel 3: transport mechanism 31: transport roller 32: transport Roller pair 33: Transport motor 4: Guide rail 5: Carriage 6: Flexi cable 7, 8: Ink receiver 100: Drive signal generator P: Recording medium PS: Recording surface

Claims (24)

Drive signal generating means for generating a drive signal including a plurality of drive pulses,
Driving pulse selecting means for selecting a driving pulse according to data of each pixel;
A head for discharging droplets from nozzles provided corresponding to the channel by changing the volume of the channel based on the selected drive pulse, and a droplet discharge device comprising:
The driving signal is a micro-vibration pulse composed of a rectangular wave as a driving pulse for micro-vibrating the meniscus in the nozzle to such an extent that droplets are not ejected from the nozzle, and having a pulse width of (2n) AL (AL is A droplet discharge device comprising a micro-vibration pulse including at least one rectangular wave having a half of an acoustic resonance period of a channel and n is an integer of 1 or more.   2. The droplet discharge device according to claim 1, wherein the fine vibration pulse includes a rectangular wave having a pulse width of 2AL.   2. The droplet discharging apparatus according to claim 1, wherein the micro-vibration pulse includes a rectangular wave having a pulse width of 1AL and 2AL.   4. The droplet discharging device according to claim 1, wherein the micro-vibration pulse is applied prior to a discharging pulse for discharging a droplet.   5. The droplet discharge device according to claim 1, wherein the (2n) AL rectangular wave is applied at least at the end of the micro-vibration pulse. 6.   6. The droplet discharge device according to claim 5, wherein a discharge pulse is applied one AL after the last applied (2n) AL rectangular wave.   The ejection pulse for ejecting the droplet includes a first pulse composed of a rectangular wave which expands the volume of the channel and returns after 1 AL, and a second pulse composed of a rectangular wave which contracts the volume of the channel and returns after a certain time. 7. The droplet discharge device according to claim 1, wherein a voltage Von of the first pulse is higher than a voltage Voff of the second pulse.   8. The droplet according to claim 7, wherein the micro-vibration pulse comprises a rectangular wave which is restored after contracting the volume of the channel, and has the same voltage as the voltage Voff of the second pulse of the ejection pulse. Discharge device.   9. The droplet discharge device according to claim 1, wherein a maximum pushing amount of the meniscus by the minute vibration pulse is equal to or less than a nozzle radius.   10. The droplet discharge device according to claim 1, wherein the head has an electromechanical conversion unit that changes the volume of the channel by applying the discharge pulse or the micro-vibration pulse.   11. The droplet discharge device according to claim 10, wherein the electromechanical conversion unit is formed of a piezoelectric material that forms a partition wall between adjacent channels and deforms in a shear mode when a voltage is applied. .   The droplet discharge device according to claim 1, wherein the droplet is ink. A drive signal including a plurality of drive pulses is generated by a drive signal generation unit,
The driving pulse is selected by the driving pulse selecting means according to the data of each pixel,
A method of driving a droplet discharge head that discharges droplets from nozzles provided corresponding to the channel by changing the volume of a channel of the droplet discharge head based on a selected drive pulse,
The driving signal is a micro-vibration pulse composed of a rectangular wave as a driving pulse for micro-vibrating the meniscus in the nozzle to such an extent that droplets are not ejected from the nozzle, and having a pulse width of (2n) AL (AL is A micro-vibration pulse including at least one rectangular wave having a half of the acoustic resonance period of the channel, where n is an integer of 1 or more), and applying the micro-vibration pulse to the droplet discharge head. A method of driving a droplet discharge head, wherein the meniscus in the nozzle is slightly vibrated to such an extent that droplets are not discharged from the nozzle.   14. The method according to claim 13, wherein the micro-vibration pulse includes a rectangular wave having a pulse width of 2AL.   14. The method according to claim 13, wherein the fine vibration pulse includes a rectangular wave having a pulse width of 1AL and 2AL.   16. The method according to claim 13, wherein the micro-vibration pulse is applied prior to a discharge pulse for discharging a droplet.   17. The method according to claim 13, wherein the (2n) AL rectangular wave is applied at least at the end of the micro-vibration pulse.   18. The method according to claim 17, wherein an ejection pulse is applied after 1AL of the (2n) AL rectangular wave applied last.   The ejection pulse for ejecting the droplet includes a first pulse composed of a rectangular wave which expands the volume of the channel and returns after 1 AL, and a second pulse composed of a rectangular wave which contracts the volume of the channel and returns after a certain time. 19. The method according to claim 13, wherein a voltage Von of the first pulse is higher than a voltage Voff of the second pulse.   20. The droplet according to claim 19, wherein the micro-vibration pulse is formed of a rectangular wave that is restored after contracting the volume of the channel, and has the same voltage as the voltage Voff of the second pulse of the ejection pulse. How to drive the ejection head.   21. The method of driving a droplet discharge head according to claim 13, wherein a maximum pushing amount of a meniscus by the fine vibration pulse is equal to or smaller than a nozzle radius.   The droplet according to any one of claims 13 to 21, wherein the droplet discharge head includes an electromechanical conversion unit that changes the volume of the channel by applying the discharge pulse or the minute vibration pulse. How to drive the ejection head.   23. The droplet discharge head according to claim 22, wherein the electromechanical conversion unit is formed of a piezoelectric material that forms a partition wall between adjacent channels and deforms in a shear mode when a voltage is applied. Drive method.   24. The method according to claim 13, wherein the droplet is ink.

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