JP2006082376A - Drive device of liquid jet head and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that it is difficult to form a large droplet by merging a plurality of droplets because a fluctuation cycle of a pressure in a liquid chamber is not constant as the fluctuation of the pressure in the liquid chamber is varied after ejection of a liquid droplet by being affected by a condition of a diaphragm in an electrostatic type liquid jet head. <P>SOLUTION: When first and second drive pulses are sequentially applied in one drive cycle, a drive waveform in the following relationship is applied. That is, a velocity of a droplet Vj takes a maximum value in a time period of ±1 μsec in the case of adopting the correlation of the velocity Vj to a liquid droplet ejected by taking as a parameter one of a time interval Td21 between the first drive pulse and second drive pulse, a rising time Tr-eff of the second drive pulse, a pulse width Pw22 and a falling time Tf-eff. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid ejection head driving apparatus and an image forming apparatus, and more particularly to a liquid ejection head and an image forming apparatus using an electrostatic actuator.

  For example, as an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, a plotter, etc., a nozzle that discharges a recording liquid droplet and a liquid chamber (discharge chamber, pressure chamber, pressurizing chamber, ink flow path) communicating with the nozzle are used. And a variable electrode constituting at least a part of the diaphragm forming the wall surface of the liquid chamber, and a counter electrode facing the variable electrode, and a voltage is applied between the electrodes. An electrostatic liquid discharge head that discharges droplets from the nozzles by displacing the variable electrode (vibration plate) with electrostatic force and generating pressure in the liquid chamber by the mechanical restoring force of the vibration plate Some are equipped as recording heads.

  In such a recording liquid discharge type image forming apparatus, gradation recording is indispensable for forming a high-quality image. Therefore, as a method for performing multi-value recording (halftone recording), a density has been conventionally used. A density modulation method that changes the density by using a plurality of inks of the same color of different colors, a dot number modulation method that modulates the dot size by forming a plurality of minute dots at substantially the same position, and a plurality of capacities ( The liquid discharge head is driven by a dot diameter modulation method that divides ink droplets (droplet volume) and modulates the size of the dots.

  Among these modulation methods, the dot number modulation method substitutes one dot with a plurality of dots, so that the dot shape becomes irregular and the image quality is not sufficient. In addition, although the density modulation method is technically difficult to achieve, it is necessary to assign a certain number of nozzles according to the increased number of ink colors, which increases the cost of the head or the nozzles of each color. As a result of reducing the number of assignments, it is inevitable that the printing speed will decrease. On the other hand, the dot diameter modulation method that separates droplets having different droplet volumes is a halftone recording method that is effective in achieving both image quality and printing speed without increasing the head cost.

Therefore, as a driving device that drives by a dot diameter modulation method using an electrostatic liquid ejection head, the pulse width of a pulse voltage (driving pulse) to be applied is conventionally changed as described in Patent Document 1, for example. As described in Japanese Patent Application Laid-Open No. 2004-260628, a plurality of pulsed driving voltages are applied and the diaphragm is restored every time the pressure fluctuation in the liquid chamber becomes positive. It is known that large droplets are ejected or combined into a large droplet during flight after being ejected.
Japanese Patent Laid-Open No. 10-193610 JP 2002-113863 A

Also, as described in Patent Document 3, after applying the first drive pulse within one drive cycle, the second drive pulse is applied at a predetermined interval, Patent Document 4 In the driving mode in which the first pulse voltage and the second pulse voltage are applied within one driving period, at least the pulse width (Pw1) and the fall time (Tf1) of the first pulse voltage or the second pulse One or two ink droplets are ejected from the nozzle by controlling the operation of the diaphragm by adjusting one or both of the voltage pulse width (Pw2) and the fall time (Tf2). What is ejected, as disclosed in Patent Document 5, is provided with at least means for applying a drive waveform in which a delay time Td from application of each pulse to application of the next pulse exceeds 2 μsec. There is also such.
JP 2001-315361 A JP 2002-96488 A JP 2002-248754 A

  However, in the driving device described in Patent Document 1 described above, when using the dot diameter modulation method, the liquid to be ejected is not limited even though the ejection speed must be constant even if the droplet amount changes. There is a problem that the ejection speed varies depending on the amount of drops.

  Further, in the driving device described in Patent Document 2, the diaphragm is only restored when the pressure fluctuation in the ink flow path is in a positive pressure state, and the pressure in the electrostatic liquid discharge head is reduced. The fluctuation period is not constant, and there is a problem that a plurality of liquid droplets cannot be merged during flight in a stable manner.

  Furthermore, in the driving devices described in Patent Documents 3 to 5, a certain limiting condition is set for the driving pulse, but here again, the pressure fluctuation period in the electrostatic liquid ejection head may not be constant. This is not considered, and there is a problem that a plurality of droplets cannot be stably merged during flight.

  In other words, the electrostatic liquid discharge head generates a discharge pressure by a mechanical force generated by deformation of a diaphragm (a variable electrode or a member including a variable electrode) that forms the wall surface of the liquid chamber. The rigidity of the plate varies greatly depending on the rigidity of the diaphragm. This is because, in a piezoelectric element type liquid discharge head that also uses a diaphragm, since the diaphragm is joined to a highly rigid member called a piezoelectric element, the rigidity of the liquid chamber has a great influence on the state of the diaphragm. It is different from not receiving.

  In this way, unlike other types of liquid discharge heads, the rigidity of the liquid chamber varies greatly depending on the state of the vibration plate, so that the vibration plate is displaced due to pressure fluctuations in the liquid chamber after droplet discharge. As a result, the pressure fluctuation cycle in the liquid chamber changes depending on the state of the diaphragm, and the pressure fluctuation cycle in the liquid chamber of the liquid discharge head as described in Patent Documents 2 to 5 is assumed to be constant. The configuration to do is not always valid, and stable merging cannot be performed to change the drop size.

  The present invention has been made in view of the above problems, and a liquid ejection head driving apparatus capable of performing stable dot-shaped modulation when performing gradation recording using an electrostatic liquid ejection head and the driving thereof An object of the present invention is to provide an image forming apparatus including the apparatus.

  In order to solve the above-described problems, the droplet ejection head drive device according to the present invention applies a drive waveform including a plurality of drive pulses within one drive cycle, so that the falling edges of the plurality of drive pulses A configuration is provided that includes means for applying a drive waveform including a plurality of drive pulses set so as to be a timing that is an integral multiple of the pressure oscillation period in the liquid chamber that changes depending on the state.

  Here, the drive waveform is a waveform in which the first and second drive pulses are sequentially applied within one drive cycle, and the time between the first drive pulse and the second drive pulse and the second drive pulse are applied. The drop velocity Vj has a maximum value within a time of ± 1 μsec when taking a correlation with the drop velocity Vj of the ejected droplet using any one of the pulse rise time, pulse width and fall time as a variable. It is preferable.

  The drive waveform is a drive waveform in which three or more drive pulses are sequentially applied within one drive cycle, and the time between adjacent drive pulses applied prior to the drive pulse and the pulse of the drive pulse. The drop velocity Vj has a maximum value within a time of ± 1 μsec when the correlation with the drop velocity Vj of the discharged droplet is taken with any of width, rise time and fall time as variables. It is preferable.

  In this case, the first applied drive pulse rise time, pulse width and fall time, the time between the first applied drive pulse and the drive pulse, the drive pulse rise time, pulse width and rise time. When each of the lowering times is set to one set, at least one set includes the time between the adjacent driving pulse applied before the driving pulse, the rise time, the pulse width, and the falling time of the drive pulse. It is preferable that the droplet velocity Vj has a maximum value within a time of ± 1 μsec when taking a correlation with the droplet velocity Vj of the ejected droplet using any one as a variable.

  An image forming apparatus according to the present invention includes a driving apparatus according to the present invention that drives a liquid ejection head that ejects droplets of a recording liquid to form an image on a recording medium.

  According to the droplet ejection head driving device and the image forming apparatus of the present invention, when a driving waveform including a plurality of driving pulses is applied within one driving cycle, the falling of the plurality of driving pulses depends on the state of the diaphragm. Since it has means to apply a drive waveform that includes multiple drive pulses set to a timing that is an integral multiple of the changing fluid chamber pressure oscillation period, multiple droplets can be merged stably to achieve high image quality An image can be formed.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, the configuration of an electrostatic liquid discharge head to which the present invention is applied will be described with reference to FIG. FIG. 1 is an explanatory cross-sectional view of the head in the lateral direction of the liquid chamber (nozzle arrangement direction).

  This liquid discharge head forms a nozzle plate 2 on which nozzles 1 for discharging recording liquid droplets are formed, a flow path plate 4 that forms a liquid chamber 3 that communicates with the nozzles 1, and a wall surface of the liquid chamber 3. A diaphragm 5 as a variable electrode and a support substrate 7 provided with a counter electrode 6 facing the diaphragm 5 as a variable electrode with a predetermined gap are provided. Here, the diaphragm 5 and the counter electrode 6 which are variable electrodes constitute an electrostatic actuator.

  The entire diaphragm 5 can be a variable electrode, or a part of the diaphragm 5 can be a variable electrode. Further, the vibration plate 5 can be formed integrally with the flow path plate 4 by anisotropic etching of a silicon substrate, or can be formed integrally with the support substrate 7 using sacrificial layer etching.

  In this liquid ejection head, an electrostatic force is generated between the diaphragm 5 and the counter electrode 6 by applying a predetermined drive pulse from the drive circuit 10 between the diaphragm 5 which is a variable electrode and the counter electrode 6. As a result, the diaphragm 5 is displaced until it comes into contact with the counter electrode 6 (the state shown in the broken line), and the electrostatic force disappears when the drive pulse falls, so that the diaphragm 5 is liquidated by its own restoring force. 6, the recording liquid (hereinafter also referred to as “ink”) in the liquid chamber 6 is pressurized by the mechanical force of the vibration plate 5, and the droplet 8 (or droplet 8 a) is discharged from the nozzle 1. , 8b, etc.) are ejected and land on the recording medium 11.

  Here, as shown in FIGS. 2A and 2B, in the case of a drive waveform in which one drive pulse (pulse voltage) is applied within one print cycle (within one drive cycle) (hereinafter referred to as “single pulse drive”). ) And a case of a driving waveform in which two driving pulses are sequentially applied (hereinafter referred to as “double pulse driving”) will be described.

  Let Mj1 be the volume of a droplet ejected by single pulse driving. On the other hand, in the double pulse drive, normally two droplets are ejected, and the total droplet volume is almost twice Mj1. Here, by applying a drive pulse having parameters described later as a drive pulse to be applied by double pulse driving, a droplet ejected from the nozzle 1 is a large 1 that is about twice as large as the droplet volume Mj1 in single pulse driving. The two droplets 8a and 8b discharged from the nozzle 1 can be merged during flight to form one droplet.

  As described above, in order to set the droplet volume that lands on the recording medium in the double pulse driving to one droplet larger than the droplet volume Mj1 in the single pulse driving, a plurality of driving pulses applied within one printing cycle are used. It falls at a timing that is an integral multiple of the pressure vibration period generated in the liquid chamber 3 due to the displacement of the variable electrode (vibrating plate 5). The plurality of droplets ejected by such a plurality of drive pulses are not only droplets larger than the droplet volume Mj1 in the single pulse drive, but are very stable against fluctuations in the drive voltage and are preferable as a liquid ejection head. Has characteristics.

  Here, in the present invention, one printing cycle (one driving cycle) is a time interval for each electrostatic actuator to form each dot on the recording medium, and is applied to the electrostatic actuator of the liquid ejection head. It is equal to the time when the drive frequency of the drive waveform is the reciprocal.

  The (liquid) droplet velocity Vj is defined by [1 mm / (time required for the droplet discharged from the nozzle to travel 1 mm)]. That is, description will be made on the assumption that the distance between the recording medium and the nozzle is 1 mm. Furthermore, it is assumed that one droplet larger than the droplet volume Mj1 at the time of single pulse driving that lands on the recording medium does not include a satellite whose droplet volume is sufficiently smaller than the main droplet. In other words, landing on the recording medium includes only one large drop, or one large drop and a satellite.

  Furthermore, the pressure vibration cycle is a cycle of pressure fluctuations generated in the liquid chamber 3 due to the displacement of the variable electrode (vibrating plate 5).

  Next, formation of large droplets by merging in the electrostatic liquid discharge head will be described. When the liquid discharge head is driven, a pressure wave (liquid density state) is generated in the liquid chamber due to a sudden volume change regardless of whether the diaphragm (variable electrode) is pulled or pushed. Due to the presence of this pressure wave, the drop velocity Vj and the pulse width Pw of the drive pulse have characteristics as shown in FIG. 3, for example. FIG. 3 shows the measurement results under the conditions of the drive pulse voltage Vp = 73 V, the diaphragm length = 1000 μm, and the ink viscosity = 3.5 m · Pa / m. Therefore, when forming a standard (one drop that is not merged), a driving pulse having a pulse width Pw around the peak of the drop velocity Vj is used.

  On the other hand, when forming a large droplet by the dot diameter modulation method, two or more drive pulses are applied. In this case, in the piezoelectric liquid ejection head, as shown in FIG. 4A, the droplet velocity Vj changes according to the pressure fluctuation period Tc in the liquid chamber, but the pressure fluctuation period Tc itself is the vibration plate. Since it does not change so much depending on the rigidity of the wall of the liquid chamber including the state, as shown in FIG. 5B, by giving a driving pulse at a constant time interval that falls at a timing that is an integral multiple of the pressure fluctuation period Tc, 2 Drops can be discharged stably.

  On the other hand, in the electrostatic liquid discharge head, the pressure fluctuation cycle changes depending on the rigidity of the wall of the liquid chamber, and the higher the rigidity, the shorter the pressure fluctuation period, and the state of the diaphragm, for example, the diaphragm faces each other. The rigidity of the liquid chamber itself changes depending on whether or not it is in contact with the counter electrode, and as a result, the pressure fluctuation period changes depending on the state of the diaphragm.

  Therefore, as shown in FIG. 5 (a), when the drop velocity Vj changes depending on the pressure fluctuation period, as shown in FIG. 5 (b), after giving the first drive pulse with the pulse width Pw1, the time Td When the second drive pulse having a pulse width Pw2 is given later and the drive pulse is lowered at an integer multiple of the pressure oscillation period, the longer the time Td between the first drive pulse and the second drive pulse, The time T (T = Td + Pw2) obtained by adding the pulse width Pw2 of the second drive pulse to the time Td between the first drive pulse and the second drive pulse becomes longer.

  In other words, in the electrostatic liquid discharge head, the pressure fluctuation cycle changes depending on the drive pulse to be applied, and the drive pulse falls at a timing that is an integral multiple of the pressure fluctuation cycle, as in the piezoelectric liquid discharge head. The simple formula does not hold, and it is not known how the pressure fluctuation period changes with the drive pulse.

  As described above, in the electrostatic liquid discharge head, if any one of the parameters of the driving pulse changes, the state of the diaphragm changes accordingly, and as a result, the pressure fluctuation period itself changes. In order to perform stable merging of parameters, it is extremely important how to set the driving pulse variables (parameters). This will be specifically described below.

Therefore, setting of drive pulse parameters will be described.
As described above, in the electrostatic liquid ejection head, in order to form a large droplet by applying a plurality of pulse voltages (drive pulses) within one printing cycle, the timing of the pressure vibration cycle generated in the liquid chamber It is preferable to apply a driving pulse that falls at (the applied pulse voltage is lowered), but as shown in FIG. 6, depending on the displacement position of the variable electrode (diaphragm), in particular, the surface on the opposite counter electrode side. Is applied (since the diaphragm 5A shown in the broken line) is not in contact with the diaphragm 5A (shown in the broken line), the rigidity of the variable electrode is greatly different and the compliance in the liquid chamber 3 changes. The pressure oscillation cycle itself changes with a slight change in the pulse voltage parameter.

This will be described with respect to double pulse driving.
First, in FIG. 2, when FIG. 2 (a) is a single pulse for forming a normal drop volume Mj1, the drive pulse forms a drop having a drop volume Mj2 that is approximately twice the drop volume Mj1. FIG. 2C shows a triple pulse that forms a droplet having a droplet volume Mj3 that is approximately three times the droplet volume Mj1, and FIG. 2D illustrates a droplet volume that is approximately N times the droplet volume Mj1. N pulses for forming MjN droplets. When a plurality of drive pulses are applied (pulse voltage set), they are generated within one printing cycle (within one driving cycle).

  The pulse voltage (drive pulse) will be described as a rectangular wave. That is, as shown in FIG. 6, in the electrostatic actuator, when the effective distance between the variable electrode (diaphragm) 5 and the counter electrode 6 in a state where no voltage is applied is eff-Gap, the variable electrode When 5 reaches the position of the diaphragm 5C displaced by the distance (eff−Gap / 3) by the voltage application, it reaches the position of the diaphragm 5C that digitally contacts the counter electrode 6 side without increasing the applied voltage value. It has the characteristic of being displaced.

  That is, in the electrostatic actuator, the variable electrode (diaphragm) 5 cannot stably maintain the displacement between the position of the diaphragm 5C and the position of the diaphragm 5B. Therefore, for example, as shown in FIG. 7A, even if the time Tr, Tf of the pulse voltage having the rise time Tr and the fall time Tf is changed, a significant behavior is caused in the electrostatic actuator. It is not possible.

  Eventually, assuming that the minimum voltage at which the variable electrode 5 contacts the opposing electrode 6 is Vth, the pulse voltage shown in FIG. 7A has a pulse width of (Tr−eff) + Pw + as shown in FIG. 7B. It can be replaced with a rectangular wave (Tf-eff). Accordingly, the rise time Tr and the fall time Tf can be considered in the same manner as the pulse width Pw. In the following description, the rise time Tr and the fall time Tf will be described as rectangular-wave drive pulses.

  As is clear from the above description, the rise time and fall time referred to in the present invention are not the rise time Tr and fall time Tf in FIG. 7A, but the time (Tr) used in FIG. -Eff) and time (T-eff).

  Thus, in each of the drive waveforms shown in FIG. 2, the single pulse drive waveform in FIG. 2A consists of only the drive pulse having the voltage value Vp and the pulse width Pw11. The drive waveform of the double pulse in FIG. 6B is the second drive pulse that is applied after the first drive pulse, which is the first drive pulse, has the voltage value Vp, the pulse width Pw21, and the first drive pulse. Is a pulse having a voltage value Vp and a pulse width Pw22. These first and second drive pulses are set to the time from the fall of the first drive pulse to the rise of the second drive pulse (this is expressed as “first This is a driving waveform output at an interval of Td21.

  Similarly, the drive waveform of the triple pulse in FIG. 5C is the second drive pulse that is applied after the first drive pulse, which is the first drive pulse, follows the voltage value Vp, pulse width Pw31, and first drive pulse. The third driving pulse to be applied subsequent to the second driving pulse is the pulse having the voltage value Vp and the pulse width Pw33, and the third driving pulse to be applied is the pulse having the voltage value Vp and the pulse width Pw33. The drive waveform is output at a time Td31 between the first and second drive pulses, and the third drive pulse is output at a time Td32 between the second and third drive pulses. is there.

  Further, in the drive waveform of the multi (N) pulse in FIG. 4D, the first drive pulse as the first drive pulse is applied following the voltage value Vp, the pulse having the pulse width PwN1, and the first drive pulse. The second drive pulse is a pulse having a voltage value Vp and a pulse width PwN2, and similarly, the Nth drive pulse is a pulse having a voltage value Vp and a pulse width PwNN. The second drive pulse is a second drive with respect to the first drive pulse. A pulse is output at a time TdN1 between the first and second drive pulses, a third drive pulse is output at a time TdN2 between the second and third drive pulses, and an Nth drive pulse is output. This is a drive waveform output at a time TdN (N-1) between the (N-1) th and Nth drive pulses.

Next, the configuration of the electrostatic actuator of the ink jet head that is the liquid discharge head used in the experiment will be described with reference to FIG.
Here, a thermal oxide film 30 is formed on a silicon substrate that is not shown, and a polysilicon 31 that is an electrode conductive layer, an HTO film 32 that is an insulating film, and a gap space 9 between the counter electrodes. As a sacrificial layer for forming, a polysilicon, an HTO film 33 serving as an insulating film, a polysilicon 34 serving as a conductive layer of a variable electrode, and a Si ₃ N ₄ film 35 having a tensile internal stress are sequentially stacked and further formed. After the film 36 is formed, the sacrificial polysilicon is removed by ICP, and finally a resin PBO layer 37 as a liquid contact layer is laminated so that the diaphragm 5 and the counter electrode 6 face each other through the gap 9. An electrostatic actuator was formed. Note that the polysilicon 31 and 34, which are conductive layers, are implanted with As to increase the electrical conductivity.

  A plurality of electrostatic actuators are integrated to form an actuator portion of an electrostatic liquid discharge head. As shown in FIG. 1, a liquid discharge head was manufactured by laminating a liquid chamber, a flow path, a flow path plate in which fluid resistance was formed, and a nozzle plate in which nozzles were formed on this actuator section.

  First, when two drive pulses are sequentially applied to the electrostatic liquid discharge head having the ejection characteristics shown in FIG. 9 when single pulse drive is performed, the fall of the two drive pulses is the state of the diaphragm. The drive waveform set so as to be an integer multiple of the pressure oscillation period in the liquid chamber that changes depending on

  An integral multiple of the pressure oscillation period in the liquid chamber when the double pulse drive is performed on the liquid discharge head can be obtained as follows. That is, the pulse width Pw21 of the first drive pulse and the time Td21 between the first and second drive pulses are appropriately selected, and the droplet velocity Vj is measured using the pulse width Pw22 of the second drive pulse as a parameter (variable). To do. Thereby, for example, the injection characteristics shown in FIG. 10 are obtained.

  At this time, the pulse width Pw22 of the second driving pulse in which the droplet velocity Vj takes the maximum value is obtained in a region where one droplet that is almost twice as large as the droplet volume Mj1 in single pulse driving is formed. In FIG. 10, the pulse width Pw22 of the second drive pulse is 9.4 μsec.

  Similarly, the result when the time Td21 between the first and second drive pulses is used as a parameter is as shown in FIG. 11, for example.

  From these FIG. 10 and FIG. 11, the double pulse parameter set [Pw21 = 7 μsec; Td21 = 5 μsec; Pw22 = 9.4 μsec] represents the time Td21 between the first and second drive pulses and the second drive pulse. It can be seen that this parameter set gives the maximum value of the drop velocity Vj when the pulse width Pw22 is used as a parameter.

  The time (Td21 + Pw22) when the droplet velocity Vj reaches the maximum value is an integral multiple of the pressure oscillation cycle in the liquid ejection head. Under the condition that the droplet velocity Vj shows the maximum value, not only the velocity is high, but also the ejection characteristic has a preferable characteristic that it is very stable against the fluctuation of the driving voltage.

  Here, the pulse width Pw21 of the first drive pulse, the time Td21 between the first and second drive pulses, and the pulse width Pw22 of the second drive pulse when the droplet velocity Vj takes the maximum value are independent of each other. Therefore, the integral multiple (Td21 + Pw22) of the pressure oscillation cycle changes when even one parameter is changed.

  An example of this is shown in FIGS. In FIG. 12, the pulse width Pw21 of the first drive pulse is 7.0 μsec, and the time Td21 between the first and second drive pulses and the pulse width Pw22 of the second drive pulse are used as parameters. It is the result of measuring speed Vj. Thus, when the time Td21 between the first and second drive pulses is changed, the optimum pulse width Pw22 of the second drive pulse also changes.

  FIG. 13 shows a parameter set in which the same measurement as in FIG. 12 is performed with the pulse width Pw21 of the first drive pulse being 7 μsec, 8 μsec, and 9.5 μsec, and the droplet velocity Vj is a maximum value.

  As can be seen from FIG. 13, even if the pulse width Pw21 of the first drive pulse is the same, the pressure oscillation period (Td21 + Pw22) is different if the time Td21 between the first and second drive pulses is different. Further, when the pulse width Pw21 of the first drive pulse is changed, the optimum pulse width Pw22 of the second drive pulse is different even when the time Td21 between the first and second drive pulses is the same. Td21 + Pw22) is a different value.

  Table 1 shows an example in which the time Td21 between the first and second drive pulses is 4 μsec.

  This is because not only whether or not the variable electrode is in contact with the opposing surface, but also the displacement shape of the variable electrode, that is, the rigidity slightly varies depending on the drive voltage value and pulse width, resulting in a change in the pressure oscillation cycle of the liquid chamber. Because.

  As described above, in the electrostatic liquid ejection head, the pressure oscillation cycle itself is changed only by slightly changing the parameter of the applied pulse voltage (drive pulse). Further, the pressure oscillation cycle varies depending on the liquid chamber shape, fluid resistance, nozzle diameter, ink viscosity, and the like. Therefore, the value of (Td21 + Pw22), which is an integral multiple of the pressure oscillation cycle, is the time Td21 between the first and second drive pulses or the pulse width Pw22 (rise time, pulse width, and fall time of the second drive pulse). The value at which the droplet velocity Vj of the ejected ink droplet takes a maximum value is experimentally derived and set.

  Here, the parameter set in the double pulse drive obtained in FIG. 13 can be adopted, but the drop velocity cannot be controlled by itself.

Therefore, the setting of the pulse width Pw21 of the first drive pulse will be described.
In the single pulse drive, when the pulse width Pw11 of the drive pulse that gives a large droplet velocity Vj is adopted as the pulse width Pw21 of the first drive pulse in the double pulse drive, the droplet velocity Vj of the droplet obtained by the double pulse drive is also relative. Become bigger. Therefore, when it is desired to increase or decrease the droplet velocity Vj in the double pulse driving, the pulse width Pw11 of the driving pulse that gives a larger or smaller droplet velocity Vj in the single pulse driving is preferably set as the pulse width Pw21 of the first driving pulse.

  Experimentally, in the single pulse drive, the pulse width of the drive pulse that gives a drop speed Vj that is about 1 m / s slower than the maximum drop speed Vj value (this is assumed to be the desired drop speed Vj in the double pulse drive). When Pw11 is set as the pulse width Pw21 of the first drive pulse, the droplet velocity Vj in the double pulse drive is approximately the same as that in the single pulse drive. In this way, it is preferable to match the droplet velocity Vj values in the single pulse drive and the double pulse drive.

  It is not always necessary to adjust the droplet velocity Vj value by the double pulse drive by such a method. That is, the droplet velocity Vj value can also be manipulated by manipulating the drive voltage Vp21 of the first drive pulse and the drive voltage Vp22 of the second drive pulse. In this case, however, (Td21 + Pw22) includes the drive conditions (including the pulse width Pw21 of the first drive pulse, the drive voltage Vp21 of the first drive pulse, and the drive voltage Vp22 of the second drive pulse). It must be an integral multiple of the pressure oscillation period of the liquid chamber. That is, when the droplet velocity Vj is measured using the time Td21 between the first and second drive pulses or the pulse width Pw22 of the second drive pulse as a parameter, the droplet velocity Vj has a maximum value in the range of ± 1 μsec. It is necessary to be. Note that a deviation within a range of ± 1 μsec is within a practical range.

Next, the setting of the time Td21 between the first and second drive pulses will be described.
If the time possessed by the entire drive pulse output by the double pulse drive is shortened as much as possible, one print cycle can be shortened and the drive frequency can be increased, so aiming to shorten (Td21 + Pw22) The time Td21 between the first and second drive pulses is preferably as short as possible. However, experimentally, when the time Td21 between the first and second drive pulses is 2 μsec or less, it is difficult to stably eject droplets. Therefore, the time Td21 between the first and second drive pulses is 2 to 6 μsec. It is particularly preferable to set the value within the range.

  Here, the error of the droplet velocity Vj that is acceptable for the liquid ejection head is up to about 0.5 m / s, and as can be seen from FIGS. 9 to 11, the time Td21 between the first and second drive pulses or the first time. If the error of the pulse width Pw22 of the second drive pulse is within ± 1 μsec, it can be said that the droplet velocity Vj value is within the allowable range.

  However, if the time Td21 between the first and second drive pulses or the pulse width Pw22 of the second drive pulse deviates more than this, not only the drop velocity Vj is greatly reduced, but also a large value to be formed by the double pulse. The number of droplets is not one, but two droplets of a normal single pulse, or an unstable discharge state.

  In this way, when using a drive waveform in which the first and second drive pulses are sequentially applied within one drive cycle, the time between the first drive pulse and the second drive pulse, the second drive pulse The droplet velocity Vj has a maximum value within a time of ± 1 μsec when taking a correlation with the droplet velocity Vj of the ejected droplet using any one of the rise time, pulse width, and fall time as variables. By applying the driving waveform, it is possible to form a large droplet in which a plurality of droplets are stably merged.

Next, a driving waveform in which three or more driving pulses are sequentially applied will be described.
Here, the drive waveform of the triple pulse in FIG. 2C in which three drive pulses are sequentially applied will be described, but the same applies to a drive waveform in which four or more (N) drive pulses are sequentially applied. The drive pulse voltage will be described as a rectangular wave from which the rise time Tr and the fall time Tf are omitted for the reason described above.

  In the case of a triple pulse, the variables (parameters) of each drive pulse (first, second, and third drive pulses) are set as follows. That is, in the double pulse drive, as described above, any one of the time between the first drive pulse and the second drive pulse, the rise time of the second drive pulse, the pulse width, and the fall time is used as a variable. When a correlation with the droplet velocity Vj of the ejected droplet is taken, a driving waveform in which the droplet velocity Vj has a maximum value within a time of ± 1 μsec is obtained.

  The following two optimum solutions satisfying the condition of this relationship [the pulse width Pw21 of the first drive pulse, the time Td21 ′ between the first and second drive pulses, the pulse width Pw22 ′ of the second drive pulse] Or [pulse width Pw21 of the first drive pulse, time Td21 "between the first and second drive pulses, and pulse width Pw22" of the second drive pulse].

  At this time, the pulse width Pw31 of the first drive pulse, the time Td31 between the first and second drive pulses, the pulse width Pw32 of the second drive pulse, the time Td33 between the second and third drive pulses, Assuming that the pulse width Pw33 of the drive pulse 3 is 3, the solution of the triple pulse [Pw31, Td31, Pw32, Td32, Pw33] is as follows.

  That is, [pulse width Pw21 of the first drive pulse, time Td21 'between the first and second drive pulses, pulse width Pw22' of the second drive pulse, time Td21 between the first and second drive pulses. ', Pulse width Pw22' of the second drive pulse "or [pulse width Pw21 of the first drive pulse, time Td21" between the first and second drive pulses, pulse width Pw22 "of the second drive pulse , Time Td21 "between the first and second drive pulses, pulse width Pw22" of the second drive pulse, or [pulse width Pw21 of the first drive pulse, time between the first and second drive pulses Td21 ′, pulse width Pw22 ′ of the second drive pulse, time Td21 ″ between the first and second drive pulses, pulse width Pw22 ″ of the second drive pulse, or [pulse width of the first drive pulse Pw2 , Time Td21 ″ between the first and second drive pulses, pulse width Pw22 ″ of the second drive pulse, time Td21 ′ between the first and second drive pulses, and pulse width Pw22 ′ of the second drive pulse ].

  This means that (Td21 + Pw22) is the basis of the pressure fluctuation cycle of the liquid chamber in the optimum parameter set obtained by the double pulse drive.

  However, in practice, it is better to use a value obtained by slightly shifting the pulse width Pw33 of the third drive pulse or the time Td32 between the second and third drive pulses (about 0.5 μsec) from the above-described solution. I know that. This is because the optimal solution experimentally obtained by the double pulse drive slightly deviates from the true solution in terms of reading error, and this deviation is amplified when the triple pulse drive is used. It is presumed that the pressure oscillation cycle of the liquid chamber formed by the first drive pulse is somewhat disturbed by the second drive pulse.

  As described above, in triple pulse driving, the pressure oscillation cycle slightly deviates from the double pulse pressure oscillation cycle.

  Since the pressure oscillation cycle is slightly shifted in this way, the value of (Td31 + Pw32 + Td32 + Pw33), which is an integral multiple of the pressure oscillation cycle, is the second and third drive pulses in triple pulse drive as in the case of double pulse drive. Using the time Td32 in the meantime or the pulse width Pw33 of the third drive pulse as a parameter, a value at which the droplet velocity Vj of the droplet ejected in the range of ± 1 μsec has a maximum value is experimentally derived and set.

  The operation of the drop velocity Vj of the large droplet formed by triple pulse driving may be performed by appropriately selecting the pulse width Pw31 of the first driving pulse, as in the case of double pulse driving. Further, according to experiments, the values of the time Td31 between the first and second drive pulses and the time Td32 between the second and third drive pulses are particularly preferably around 2 to 6 μsec.

Accordingly, a driving waveform for the liquid discharge head having the ejection characteristics shown in FIG. 14 by single pulse driving will be described.
As shown in FIG. 15, in the double pulse driving, two parameter sets that give the maximum value to the droplet velocity Vj are shown in Table 2. Note that the droplet volume Mj in the double pulse drive is about twice the value of the droplet volume in the single pulse drive.

  Next, based on these two parameter sets, the pulse width Pw31 of the first drive pulse, which is a triple pulse drive parameter, the time Td31 between the first and second drive pulses, and the pulse width of the second drive pulse Taking the time Td32 between Pw32 and the second and third drive pulses as shown in Table 3, and using the pulse width Pw33 of the third drive pulse as a parameter, the droplet velocity Vj and droplet volume Mj of the ejected large droplet are The measured results are also shown in Table 3.

  Thus, the optimum pulse width Pw33 of the third drive pulse is the time between the second drive pulse that is an adjacent drive pulse applied prior to the third drive pulse, that is, the second, It can be seen that this depends on the time Td32 between the third drive pulses.

  In the double pulse drive, (Td21 + Pw22) which is an integral multiple of the pressure vibration cycle is substantially an integral multiple of the pressure vibration cycle even in the triple pulse drive.

  As described above, when a driving waveform in which three or more driving pulses from the first to the Nth are sequentially applied in one driving cycle is used, the time between adjacent driving pulses applied before the driving pulse is used. In addition, the drop velocity Vj is maximized within a time of ± 1 μsec when taking a correlation with the drop velocity Vj of the ejected droplet using any one of the pulse width, rise time and fall time of the drive pulse as a variable. By applying a drive waveform having a value, a large droplet in which a plurality of droplets are stably merged can be formed.

  In other words, using the parameter definitions in the drive waveforms of FIGS. 2C and 2D described above, the first pulse voltage is expressed as [Voltage value = VpN1, Rise time = TrN1, Pulse width = PwN1, Fall time. = TfN1], the Nth pulse voltage is [voltage value = VpNN, rise time = TrNN, pulse width = PwNN, fall time = TfNN], and the (N−1) th and Nth pulse voltages Assuming that the time is TdN (N-1), if one of PwNN, TrNN, TfNN, and TdN (N-1) is used as a parameter and the correlation with the ejected droplet velocity Vj is taken, it is in the range of ± 1 μsec. That is, the drop velocity Vj has a maximum value.

  In this case, the drive pulse rise time, pulse width and fall time applied first, the time between the drive pulse applied first and the drive pulse, drive pulse rise time, pulse width And at least one set includes a time between the adjacent drive pulse applied before the drive pulse, a rise time, a pulse width, and a fall of the drive pulse. It is preferable that the droplet velocity Vj has a maximum value within a time of ± 1 μsec when taking a correlation with the droplet velocity Vj of the ejected droplet with any one of the times as a variable.

  In other words, when the parameter definition in the drive waveform of FIG. 2D is used, [TrN1, PwN1, TfN1, TdN1, TrN2, PwN2, TfN2], [TrN1, PwN1, TfN1, TdN2, TrN3, PwN3, TfN3 ], [TrN1, PwN1, TfN1, Td (N-1), TrNN, PwNN, TfNN] at least one of the parameter sets is TdNj, PwNi, TrNi, TfNi (i = 2 to N; Taking one of j = i−1) as a parameter and taking a correlation with the ejected droplet velocity Vj, the droplet velocity Vj has a maximum value in a range of ± 1 μsec.

Next, an example of the image forming apparatus according to the present invention on which the liquid ejection head driving device according to the present invention is mounted will be described with reference to FIGS. FIG. 17 is an explanatory side view for explaining the overall configuration of the image forming apparatus according to the present invention, and FIG. 18 is an explanatory plan view of a main part of the apparatus.
In this image forming apparatus, a carriage 103 is slidably held in a main scanning direction by a guide rod 101 and a guide rail 102 which are horizontally mounted on left and right side plates (not shown), and a timing belt 105 is slid by a main scanning motor 104. 17 is moved and scanned in the direction indicated by the arrow (main scanning direction) in FIG.

  On this carriage 103, for example, four recording heads 107 each comprising a droplet discharge head according to the present invention for discharging yellow (Y), cyan (C), magenta (M), and black (Bk) ink droplets, respectively. Are arranged in a direction crossing the main scanning direction and the ink droplet discharge direction is directed downward.

  As described above, the electrostatic liquid discharge head is used as the liquid discharge head constituting the recording head 107. Note that the recording head can also be configured by one or a plurality of liquid ejection heads provided with a plurality of nozzle rows that eject different colors.

  The carriage 103 is equipped with a sub tank 108 for each color for supplying each color ink to the recording head 107. Ink is supplied to the sub tank 108 from a main tank (ink cartridge) (not shown) via an ink supply tube 109.

  On the other hand, as a paper feeding unit for feeding paper 112 stacked on a paper stacking unit (pressure plate) 111 such as a paper feeding cassette 110, a half-moon roller (separately feeding paper 112 one by one from the paper stacking unit 111) A separation pad 114 made of a material having a large friction coefficient is provided opposite to the sheet feeding roller 113 and the sheet feeding roller 113, and the separation pad 114 is urged toward the sheet feeding roller 113 side.

  As a transport unit for transporting the paper 112 fed from the paper feed unit below the recording head 107, a transport belt 121 for electrostatically attracting and transporting the paper 112, and a paper feed unit A counter roller 122 for transporting the paper 112 fed through the guide 115 while sandwiching it between the transport belt 121 and the paper 112 fed substantially vertically upward is changed by about 90 ° and copied on the transport belt 121. A conveying guide 123 for adjusting the pressure and a tip pressure roller 125 urged toward the conveying belt 121 by a pressing member 124. In addition, a charging roller 126 that is a charging unit for charging the surface of the conveyance belt 121 is provided.

  Here, the conveyance belt 121 is an endless belt, is stretched between the conveyance roller 127 and the tension roller 128, and the conveyance roller 127 is rotated from the sub-scanning motor 131 via the timing belt 132 and the timing roller 133. By doing so, it is configured to circulate in the belt conveyance direction (sub-scanning direction) of FIG. A guide member 129 is disposed on the back side of the conveyance belt 121 in correspondence with the image forming area formed by the recording head 107.

  As shown in FIG. 11, a slit disk 134 is attached to the shaft of the transport roller 127, and a sensor 135 for detecting the slit of the slit disk 134 is provided. An encoder 136 is configured.

  The charging roller 126 is arranged so as to contact the surface layer of the conveyor belt 121 and rotate following the rotation of the conveyor belt 121, and applies 2.5N to both ends of the shaft as a pressing force.

  Further, as shown in FIG. 17, an encoder scale 142 having slits is provided on the front side of the carriage 103, and an encoder sensor composed of a transmissive photosensor that detects the slits of the encoder scale 142 on the front side of the carriage 103. The encoder 144 for detecting the position of the carriage 103 in the main scanning direction is configured by these.

  Further, as a paper discharge unit for discharging the paper 112 recorded by the recording head 107, a separation unit for separating the paper 112 from the conveying belt 121, a paper discharge roller 152 and a paper discharge roller 153, and paper discharge A paper discharge tray 154 for stocking the paper 112 to be printed.

  A double-sided paper feeding unit 161 is detachably attached to the back. The double-sided paper feeding unit 161 takes in the paper 112 returned by the reverse rotation of the transport belt 121, reverses it, and feeds it again between the counter roller 122 and the transport belt 121.

  Further, as shown in FIG. 18, a maintenance / recovery mechanism 191 for maintaining and recovering the state of the nozzles of the recording head 107 is disposed in a non-printing area on one side of the carriage 103 in the scanning direction.

  The maintenance and recovery mechanism 191 caps each nozzle surface of the recording head 107 (here, “nozzle surface” refers to the outermost surface of the nozzle plate 13, that is, the surface of the fluorine-based water repellent layer 65 or the surface of the silicone resin 75). Caps 192a to 192d (referred to as “cap 192” when not distinguished), a wiper blade 193 that is a blade member for wiping the nozzle surface, and recording to discharge the thickened recording liquid An empty discharge receptacle 194 for receiving droplets when performing empty discharge for discharging droplets that do not contribute is provided.

  In the image forming apparatus configured as described above, the sheets 112 are separated and fed one by one from the sheet feeding unit, and the sheet 112 fed substantially vertically upward is guided by the guide 115, and includes the conveyance belt 121 and the counter roller 122. The leading end is guided by the conveying guide 123 and pressed against the conveying belt 121 by the leading end pressure roller 125, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately repeated from the high voltage power source to the charging roller 126 by a control circuit (not shown), that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 21 is alternating, that is, In the sub-scanning direction, which is the circumferential direction, plus and minus are alternately charged in a band shape with a predetermined width. When the paper 112 is fed onto the conveyance belt 121 charged alternately with plus and minus, the paper 112 is attracted to the conveyance belt 121 by electrostatic force, and the paper 112 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 121. Is done.

  Therefore, by driving the recording head 107 according to the image signal while moving the carriage 103, ink droplets are ejected onto the stopped paper 112 to record one line, and after the paper 112 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 112 has reached the recording area, the recording operation is finished, and the paper 112 is discharged onto the paper discharge tray 154.

  In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 112 is fed into the double-sided paper feeding unit 161 by rotating the conveyor belt 121 in the reverse direction. The paper 112 is reversed (with the back surface being the printing surface), and is fed again between the counter roller 122 and the conveyor belt 121. The timing is controlled, and the sheet is conveyed onto the conveyor bell 121 as described above. After recording on the back side, the sheet is discharged to the discharge tray 154.

  Further, during printing (recording) standby, the carriage 103 is moved to the maintenance / recovery mechanism 191 side, the nozzle surface of the recording head 107 is capped by the cap 192, and the nozzles are kept in a wet state. To prevent. In addition, the recording liquid is sucked from the nozzle in a state where the recording head 107 is capped with the cap 192 (referred to as “nozzle suction” or “head suction”), and a recovery operation is performed to discharge the thickened recording liquid or bubbles. Wiping is performed by the wiper blade 193 in order to clean and remove ink adhering to the nozzle surface of the recording head 107 by this recovery operation. In addition, an idle ejection operation for ejecting ink not related to recording is performed before the start of recording or during recording. Thereby, the stable ejection performance of the recording head 107 is maintained.

Next, an outline of the control unit of the image forming apparatus will be described with reference to FIG. This figure is an overall block diagram of the control unit.
The control unit 200 includes a CPU 201 that controls the entire apparatus, a ROM 202 that stores programs executed by the CPU 201 and other fixed data, a RAM 203 that temporarily stores image data, and the like, while the apparatus is powered off. 1 includes a non-volatile memory (NVRAM) 204 for holding data, an image processing for performing various signal processing and rearrangement on image data, and an ASIC 205 for processing input / output signals for controlling the entire apparatus. Yes.

  The control unit 200 also has an I / F 206 for transmitting and receiving data and signals to and from the host, which is an image processing apparatus (or data processing apparatus) such as a personal computer, and a drive for driving the recording head 107. A drive waveform generation unit 207 that generates a waveform, a head driver 208 that drives and controls the recording head 107, a main scanning motor drive unit 211 that drives the main scanning motor 104, and a sub-scan motor 131 that drives the sub-scanning motor 131. Inputs detection signals from a scanning motor driving unit 213, an AC bias supply unit 214 that supplies an AC bias voltage to the charging roller 126, an environmental sensor 218 that detects environmental temperature and / or environmental humidity, and various sensors (not shown). I / O 216 and the like are provided.

  The control unit 200 is connected to an operation panel 217 for inputting and displaying information necessary for the apparatus.

  Here, the control unit 200 transmits print data (print data) including image data from the host side such as an image processing apparatus such as a personal computer, an image reading apparatus such as an image scanner, an imaging apparatus such as a digital camera, or the like. The data is received by the I / F 206 via the net.

  The CPU 201 reads and analyzes the print data in the reception buffer included in the I / F 206, performs necessary image processing, data rearrangement processing, and the like in the ASIC 205, and transfers the image data to the head driver 208. The dot pattern data for image output may be generated by storing font data in the ROM 202, for example, or the image data is developed into bitmap data by a host-side printer driver and transferred to this apparatus. You may do it.

  The drive waveform generation unit 207 includes a D / A converter that performs D / A conversion on the drive pulse pattern data, and has a drive waveform composed of one drive pulse and a plurality of drive pulses that satisfy the above-described conditions. Output to the driver 208.

  The head driver 208 selectively records a drive pulse constituting a drive waveform supplied from the drive waveform generation unit 207 based on image data (dot pattern data) corresponding to one line of the recording head 107 input serially. The head is driven by being applied between the diaphragm of the head 7 and the counter electrode.

  This control unit constitutes a drive device according to the present invention in which a drive waveform is applied to a recording head, which is a liquid ejection head, by a drive waveform generation unit 207 and a head driver 208. Therefore, large droplets can be formed stably, gradation recording with high image quality is possible, and both printing speed and image quality can be achieved.

FIG. 5 is a cross-sectional explanatory view along the lateral direction of the liquid chamber showing an example of an electrostatic liquid discharge head to which the present invention is applied. It is explanatory drawing which shows the example from which the drive pulse which comprises the drive waveform used for the drive of the head differs. It is explanatory drawing explaining the characteristic of the droplet speed Vj and the pulse width of a drive pulse similarly. It is explanatory drawing with which it uses for description of the large droplet formation conditions in a piezoelectric type liquid discharge head. It is explanatory drawing with which it uses for description of the large droplet formation conditions in an electrostatic liquid discharge head. It is explanatory drawing with which it uses for description of the behavior of the diaphragm in an electrostatic type liquid discharge head. It is explanatory drawing with which it uses for description of the drive pulse waveform with respect to an electrostatic liquid discharge head. It is explanatory drawing with which it uses for description of the specific structure of the electrostatic actuator part of the electrostatic liquid discharge head used for experiment. It is explanatory drawing which shows an example of the relationship between the pulse width and droplet speed in single pulse drive. It is explanatory drawing which shows an example of the relationship between the pulse width of the 2nd drive pulse and droplet speed in double pulse drive. It is explanatory drawing which shows an example of the relationship between the time between the 1st, 2nd drive pulse in a double pulse drive, and drop speed. It is explanatory drawing which shows an example of the relationship between the pulse width of the 2nd drive pulse in double pulse drive, the time between the 1st, 2nd drive pulse, and drop velocity. It is explanatory drawing with which it uses for description of the required time of a double pulse waveform set. It is explanatory drawing which shows the other example of the relationship between the pulse width and droplet speed in single pulse drive. It is explanatory drawing which shows an example of the relationship between the pulse width of the 2nd drive pulse and droplet speed in a double pulse drive similarly. Similarly, in triple pulse driving, an explanation is given of an example of the relationship between the time between the first and second driving pulses, the time between the second and third driving pulses, the pulse width of the third driving pulse and the droplet velocity. FIG. 1 is an explanatory side view illustrating an overall configuration of an image forming apparatus according to the present invention. FIG. 2 is an explanatory plan view of a main part of the image forming apparatus. 2 is a block diagram illustrating an overview of a control unit of the image forming apparatus. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Nozzle 2 ... Nozzle plate 3 ... Liquid chamber 4 ... Flow path plate 5 ... Vibration plate 6 ... Counter electrode 207 ... Drive waveform generation part 208 ... Driver

Claims (5)

  A nozzle that ejects droplets of the recording liquid, a liquid chamber that communicates with the nozzle, a variable electrode that forms at least a part of a diaphragm that forms a wall surface of the liquid chamber, and a counter electrode that faces the variable electrode, When the driving pulse is applied between the electrodes, the vibration plate is displaced, and a droplet is discharged from the nozzle by a mechanical force. In a driving device that drives a liquid discharge head that changes depending on the state, when a driving waveform including a plurality of driving pulses is applied within one driving cycle, the falling of the plurality of driving pulses changes depending on the state of the diaphragm A liquid ejection head drive device comprising: means for applying a drive waveform including the plurality of drive pulses set so as to have a timing that is an integral multiple of the indoor pressure oscillation period.   2. The liquid ejection head drive device according to claim 1, wherein the drive waveform is a waveform in which first and second drive pulses are sequentially applied within one drive cycle, and the first drive pulse and the first drive pulse are applied. When the correlation between the time between the two drive pulses and the drop velocity Vj of the ejected droplet is taken with any one of the rise time, pulse width and fall time of the second drive pulse as a variable. A driving apparatus for a liquid discharge head, wherein the droplet velocity Vj has a maximum value within a time of ± 1 μsec.   2. The liquid ejection head drive device according to claim 1, wherein the drive waveform is a drive waveform in which three or more drive pulses are sequentially applied within one drive cycle, and is adjacently applied prior to the drive pulse. A time of ± 1 μsec when taking a correlation with the drop velocity Vj of a droplet to be discharged with any one of the time between the drive pulse and the pulse width, rise time, and fall time of the drive pulse as a variable A liquid ejection head driving device characterized in that the droplet velocity Vj has a maximum value.   In the driving apparatus of the liquid ejection head according to claim 3, the rising time, the pulse width and the falling time of the first driving pulse, the time between the first driving pulse and the driving pulse, When the drive pulse rise time, the pulse width, and the fall time are set as one set, at least one set includes the time between the drive pulse applied before the drive pulse and the drive pulse. When any one of the rise time, pulse width, and fall time is used as a variable, and the correlation with the drop velocity Vj of the discharged droplet is taken, the drop velocity Vj has a maximum value within a time of ± 1 μsec. A drive device for a liquid discharge head. 5. An image forming apparatus equipped with a liquid ejection head for ejecting recording liquid droplets to form an image on a recording medium, comprising the liquid ejection head drive device according to any one of claims 1 to 4. An image forming apparatus.

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