JP2007276420A - Method for driving liquid droplet delivering and recording head, and liquid droplet delivering and recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for driving a liquid droplet delivering and recording head which can correct scattering of the volumes of ink droplets between heads and in a delivering mechanism in the head by using binary digital driving wave form without upsizing of a driving circuit and increasing in cost. <P>SOLUTION: Respective delivering mechanisms are classified into either a high rank group, a middle rank group or a low rank group in which ranges of the volumes of ink droplets delivered by the same driving wave form are respectively different. The pulse width where the volume of the liquid droplet becomes maximum when one pulse is applied on a piezoelectric element 42 by using the low rank group as an object is set in advance as the pulse width for the driving wave form for the large droplet. When the driving wave form for the large droplet is applied on the piezoelectric element 42 by using the delivering mechanism of the other group as an object, the pulse width wherein the volume of the liquid droplet is the same as the maximum volume of the liquid droplet of the delivering mechanism of the low rank group, and the pulse width which is smaller than the pulse width where the volume of the liquid droplet delivered becomes maximum are set in advance as the pulse width of the driving wave form for the large droplet. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a droplet discharge recording head driving method for recording an image by discharging droplets, and a droplet discharge recording apparatus including the droplet discharge recording head.

  2. Description of the Related Art Conventionally, a droplet discharge recording apparatus such as an ink jet printer that discharges droplets such as ink droplets from a discharge nozzle provided in a droplet discharge recording head and records an image on a recording medium is known.

  Examples of droplet discharge methods include those that rapidly heat a liquid to generate bubbles and discharge droplets using the pressure, and those that apply a drive voltage waveform to a piezoelectric element to generate pressure waves and discharge droplets, etc. is there.

  In a droplet discharge recording apparatus using piezoelectric elements, different drive voltage waveforms corresponding to the density of dots to be recorded are applied to the piezoelectric elements corresponding to a plurality of nozzles of a droplet discharge recording head for each pixel. The gradation expression is performed by adjusting the volume of the ejected droplet. Conventionally, an analog drive waveform is often used as the drive voltage waveform because of the controllability of droplet ejection. In this type of droplet discharge recording apparatus, the voltage amplitude and time change can be arbitrarily set by using an analog drive waveform as the drive voltage waveform, so that the modulation range of the droplet volume to be discharged can be increased, and a desired It is also easy to discharge a droplet of a droplet amount. However, in order to use the analog drive waveform, there is a problem that the drive circuit becomes large and the power consumption is large. In particular, this problem has become prominent in a recording apparatus using a paper-width long head aimed at speeding up.

  Thus, there is a droplet discharge recording apparatus that uses a binary digital drive waveform for the purpose of downsizing, cost reduction, and energy saving of the drive circuit. However, with this binary digital drive waveform, the degree of freedom of the drive voltage waveform is greatly reduced, and it is very difficult to adjust to a desired droplet amount. For this reason, various techniques for adjusting the volume of ejected droplets using binary digital drive waveforms have been proposed.

  By the way, there are variations in manufacturing of the droplet discharge recording heads, and there are variations in the discharge characteristics of the droplets between the recording heads and in the discharge mechanism within the same recording head, and even if the same drive waveform is applied, the droplets are discharged. Variations in the volume and speed of the liquid droplets. Such variation in droplet volume causes uneven density of the image, and variation in droplet velocity causes displacement of the landing position of the droplet, resulting in degradation of image quality.

  The main causes of variations in the discharge characteristics are divided into two types: variations in the natural vibration period of fluid vibration due to variations in the dimensions of the discharge nozzle flow path and the rigidity of the pressure chamber, and variations in the energy conversion efficiency of the piezoelectric element. It is done.

  Conventionally, in a recording head driven using a digital drive waveform, it has been proposed to change the pulse width of the drive waveform for each nozzle according to the distance between the nozzle driven simultaneously and the nozzle (for example, Patent Document 1).

  Japanese Patent Application Laid-Open No. 2004-228620 proposes correcting the drive voltage for each nozzle in accordance with the variation among nozzles, the number of drive pulses, the temperature, and the like.

In the analog waveform, for the variation between the heads, the drive waveform is set for each head, the variation of the natural vibration period is in the time direction of the drive waveform, and the efficiency conversion variation of the piezoelectric element is in the voltage direction of the drive waveform, respectively. Although the correction was made, the variation in the ejection mechanism in the head could not be corrected because the drive circuit further increased in size.
JP-A-4-357036 JP 2002-205397 A

  However, in the technique described in Patent Document 1, the pulse width is changed for each ejection mechanism in the digital waveform, but there is no description regarding a specific correction method for manufacturing variations for each ejection mechanism. Further, the technique described in Patent Document 2 has a problem in that it is necessary to provide a plurality of types of power supply voltages in order to change the drive voltage, which increases the size of the drive circuit and increases costs.

  The present invention has been made to solve the above-described problems, and uses a binary digital drive waveform to produce variations in the ejection mechanism between the heads and in the head without increasing the size of the drive circuit and increasing the cost. It is an object of the present invention to provide a droplet discharge recording head driving method and a droplet discharge recording apparatus capable of correcting variations in ink droplet volume and ink droplet velocity caused by the above.

  In order to solve the above-mentioned problems, the invention of claim 1 includes a pressure chamber in which a discharge port is provided and a liquid is accommodated therein, and a piezoelectric device driven by applying a pulse signal which is a binary digital drive waveform. A plurality of elements that apply a pulse signal to the piezoelectric element to drive the piezoelectric element, thereby applying a vibration wave to the liquid contained in the pressure chamber and discharging droplets from the discharge port. A droplet discharge recording head driving method in which each discharge mechanism has a two-dimensional characteristic in which the pulse width-droplet volume characteristic has a maximum point, and the piezoelectric elements constituting each discharge mechanism Each discharge mechanism is classified into at least two types of groups according to the difference in pulse width-droplet volume characteristics of each discharge mechanism due to the difference in the electrical conversion efficiency of the element, and one pulse is generated between each group for each group. Discharged by application When setting the pulse width for discharging one pulse droplet so that the droplet volumes are equal, relative to the pulse width of the lower rank group including the discharge mechanism having relatively poor electrical conversion efficiency, In particular, the pulse width of the higher rank group is set to be narrow.

  According to the first aspect of the present invention, focusing on the fact that the pulse width-droplet volume characteristic of each ejection mechanism exhibits a quadratic function characteristic having a maximum point, the electrical conversion of the piezoelectric element constituting each ejection mechanism Each ejection mechanism is classified into at least two groups according to the difference in pulse width-droplet volume characteristics of each ejection mechanism due to the difference in efficiency.

  Here, when the electromechanical conversion efficiency of the piezoelectric element is poor, the amount of displacement when a drive voltage having a standard voltage amplitude is applied is small, so that the droplet volume becomes small or the droplet velocity becomes slow. For this reason, in claim 1, the group into which the ejection mechanisms constituted by piezoelectric elements having poor electromechanical conversion efficiency are classified as a low-rank group.

  According to the first aspect of the present invention, when the pulse width for discharging one pulse droplet is set so that the droplet volume discharged by applying one pulse is equal between the groups for each group. Further, by setting the pulse width of the group on the higher rank side to be relatively narrower than the pulse width of the group on the lower rank side including the ejection mechanism having relatively low electrical conversion efficiency, 2 By using the digital driving waveform of the value, it is possible to correct the variation in the ink droplet volume between the heads and in the ejection mechanism in the head without increasing the size of the driving circuit and increasing the cost.

  That is, it is known from experiments and the like that the characteristics of the droplet volume with respect to the pulse width and the characteristics of the droplet velocity both exhibit characteristics having local maximum points, but the local maximum points and shapes of both characteristics do not match. Paying attention to the difference between the characteristics of the droplet volume and the velocity of the droplet with respect to the pulse width, the pulse width of the high-rank group is a pulse with a droplet volume equivalent to the droplet volume on the low-rank side. Of the widths, the pulse width smaller than the pulse width that maximizes the droplet volume of the higher-rank group is selected. An increase can be prevented.

  According to the present invention, as in the second aspect of the present invention, the pulse width at which the droplet volume becomes the maximum point is applied as a pulse signal for discharging one pulse droplet in the group having relatively low characteristics. You may make it do.

  According to the second aspect of the present invention, in realizing the first aspect of the invention, for the low rank group, the pulse width is set so as to exhibit the maximum performance based on the characteristics, and the high rank side is set. For this group, the performance is appropriately adjusted in a range in which the pulse width is narrower than the pulse width of the lower rank group according to the characteristics of the lower rank group, so that the overall energy efficiency is improved. .

  Further, according to the second aspect of the present invention, as in the third aspect of the present invention, the pulse width at which the droplet volume becomes a maximum point is ½ times the natural vibration period of the liquid flow in the liquid flow path. Preferably there is.

  On the other hand, in order to solve the above-mentioned problem, the invention of claim 4 is driven by a pressure chamber provided with a discharge port and containing liquid and a pulse signal which is a binary digital drive waveform is applied. A piezoelectric element is applied to the piezoelectric element, and a pulse signal is applied to the piezoelectric element to drive the piezoelectric element, thereby applying a vibration wave to the liquid contained in the pressure chamber and discharging a droplet from the discharge port. A method of driving a droplet discharge recording head having a plurality of discharge mechanisms, wherein each of the discharge mechanisms corresponds to a droplet volume discharged when a pulse signal having the same pulse width is applied to each piezoelectric element. When the pulse width of one pulse is set for each group so that the droplet volume is classified into a plurality of groups and the droplet volume when one pulse is applied becomes a predetermined droplet volume, the discharge with the smallest droplet volume is performed. Low rank guru including mechanism Than the pulse width of the flops is characterized by setting so that the pulse width of the other group is narrowed.

  According to the invention of claim 4, the ejection mechanism is classified into a plurality of groups according to the droplet volume ejected when a pulse signal having the same pulse width is applied to each piezoelectric element, and one pulse is applied. Since the pulse width of one pulse is set for each group so that the droplet volume at that time becomes a predetermined droplet volume, a binary digital drive waveform can be used without changing the drive waveform in the voltage direction. Variations in droplet volume between the heads and in the ejection mechanism in the head can be corrected only by changing in the time direction.

  According to the invention of claim 4, since the setting is made so that the pulse width of the other group becomes narrower than the pulse width of the low rank group including the discharge mechanism having the smallest droplet volume, Regardless, the droplet volumes can be matched with high accuracy.

  In other words, paying attention to the difference between the characteristics of the droplet volume and the droplet velocity with respect to the pulse width, the pulse widths of the other groups are made narrower than the pulse widths of the lower rank groups. It is possible to prevent an increase in droplet velocity difference due to correction of volume variation.

  According to a fourth aspect of the present invention, as in the fifth aspect of the present invention, as a pulse width of a low rank group including an ejection mechanism having the smallest droplet volume, one pulse is applied to the piezoelectric element for the low rank group. The pulse width that maximizes the droplet volume when applied is set.

  According to the fifth aspect of the present invention, the pulse width that maximizes the droplet volume is applied as the pulse width of the low rank group, and the droplet volume of the discharge mechanism of the other group is the same as that of the discharge mechanism of the low rank group. Since the setting is made so as to match the droplet volume, the droplet volumes of the ejection mechanisms of all the groups can be made to coincide with each other without difficulty.

  Further, in the invention according to any one of claims 1 to 5, as in the invention according to claim 6, a group having a higher droplet velocity in accordance with a difference in droplet velocity between the groups. The application timing of the one pulse may be delayed.

  Further, according to the present invention, as in the seventh aspect of the invention, in the invention of any one of the first to sixth aspects, two pulses are applied to the piezoelectric element at predetermined intervals. When droplets are ejected, variations in droplet volume can be corrected by changing the interval for each group.

  In the present invention, it is preferable that the intervals are different so that the sum of the interval and the pulse width of the second pulse is constant.

  According to the present invention, as in the ninth aspect of the invention, a plurality of the droplet discharge recording heads are provided, and variations in droplet discharge characteristics between the droplet discharge recording heads can be corrected.

  Further, according to the present invention, as in the invention described in claim 10, the pulse is a first step of expanding the pressure chamber by falling from the bias voltage, and the voltage is kept constant and the pressure chamber is expanded. You may make it consist of the 2nd process to maintain, and the 3rd process which contracts a pressure chamber to the original position by rising to a bias voltage.

  On the other hand, in order to solve the above-mentioned problem, the invention of claim 11 is driven by a pressure chamber provided with a discharge port and containing liquid therein and a pulse signal which is a binary digital drive waveform is applied. A piezoelectric element is applied to the piezoelectric element, and a pulse signal is applied to the piezoelectric element to drive the piezoelectric element, thereby applying a vibration wave to the liquid contained in the pressure chamber and discharging a droplet from the discharge port. A droplet discharge recording head having a plurality of discharge mechanisms to be categorized, and each of the discharge mechanisms is classified into a plurality of groups corresponding to the droplet volume discharged when a pulse signal having the same pulse width is applied to each piezoelectric element. A storage means for storing the classified data, and a group other than the pulse width of the low-rank group including a discharge mechanism in which the droplet volume when one pulse is applied becomes a predetermined droplet volume and the droplet volume is the smallest A control unit that applies a table pulse width that is set in advance to a group in which each ejection mechanism is classified when applying a pulse to the piezoelectric element and a table that is set to have a narrow pulse width. And.

  According to the eleventh aspect of the invention, since it operates in the same manner as the fourth aspect, the binary digital drive waveform is used similarly to the fourth aspect of the invention, resulting in an increase in size and cost of the drive circuit. Thus, it is possible to correct variations in ink droplet volume between the heads and in the ejection mechanism in the head.

  As described above, according to the present invention, ink droplets in the ejection mechanism between the heads or in the head can be used only by changing in the time direction without changing the drive waveform in the voltage direction using the binary digital drive waveform. Because volume variation is corrected, binary digital drive waveforms can be used to correct ink droplet volume variations between heads and in the ejection mechanism within the head without increasing the size of the drive circuit and increasing costs. It has the effect.

  In addition, according to the present invention, there is an effect that variations in ink droplet volume can be corrected without increasing the ink droplet velocity difference more than necessary.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Hereinafter, a case where the present invention is applied to an inkjet printer will be described.

  FIG. 1 schematically shows the configuration of an ink jet printer (hereinafter simply referred to as “printer”) 10 according to the present embodiment.

  As shown in the figure, an endless conveying belt 12 is wound around a plurality of rollers 14 around the printer 10 and circulates in a direction indicated by an arrow A in the drawing. A part of the plurality of rollers 14 is a driving roller that rotates by receiving a driving force (not shown), and the other roller is a driven roller that rotates following the rotation of the conveyor belt 12. Yes.

  On the other hand, a paper tray 20 is disposed in the printer 10, and recording paper P for recording images is stacked and stored in the paper tray 20. The recording paper P stored in the paper tray 20 is taken out one sheet at a time from the uppermost layer by a pickup mechanism (not shown) and guided to the paper feed transport path 22, and the paper feed transport path 22 performs predetermined recording on the transport belt 12. Sent to position. The transport belt 12 has a function of holding the recording paper P in close contact. As a result, the recording paper P fed through the paper feed conveyance path 22 is conveyed in the direction of the arrow A while being held in close contact.

  In the printer 10, a recording head unit 37 is disposed along the conveyance path of the recording paper P on the downstream side in the conveyance direction of a predetermined position where the recording paper P is fed onto the conveyance belt 12. In this recording head unit 37, cyan (C) color ink discharge, magenta (M) color ink discharge, yellow (Y) color ink discharge, black ink are discharged from the upstream side in the conveyance direction of the recording paper P by the conveyance belt 12. (K) Four recording heads 36 for color ejection are provided, and the recording paper P conveyed is sequentially opposed to the recording heads 36 for each color.

  Each color recording head 36 has an FWA (Full Width Array) in which a large number of ink ejection nozzles 40 (not shown in FIG. 1, refer to FIG. 2) are arranged over the entire width direction of the conveying belt 12 orthogonal to the arrow A direction. It is supposed to be of a type.

  Each recording head 36 is driven by a recording head control unit 50, and ink droplets of each color are ejected from ink ejection nozzles 40 provided on each recording head 36 based on image data. As a result, ink droplets are sequentially ejected by the recording heads 36 facing each other onto the recording paper P that is in close contact with the conveying belt 12 to record a full-color image.

  Further, on the transport path of the recording paper P by the transport belt 12 and on the downstream side of the recording head unit 37, the scraper 26 corresponds to the arrangement position of the rollers 14 provided at the position where the transport path is bent. The recording paper P on which image recording has been completed is separated from the transport belt 12 and sent to the paper discharge tray 30 via the discharge path 28.

  FIG. 2 is a cross-sectional view of the recording head 36 according to the present embodiment.

  As shown in the figure, the recording head 36 includes an ink discharge nozzle 40, an ink tank 41, a supply path 44, a pressure chamber 46, and a piezoelectric element 42. At least one piezoelectric element 42 and one pressure chamber 46 are provided for each ink ink discharge nozzle 40, and constitute a discharge mechanism 35.

  An appropriate amount of ink is supplied to the ink tank 41 from an ink cartridge (not shown) of a color corresponding to each recording head 36 and temporarily stored. The ink tank 41 communicates with the pressure chamber 46 via the supply path 44, and the pressure chamber 46 communicates with the outside via the ink discharge nozzle 40.

  A part of the wall surface of the pressure chamber 46 is constituted by a pressure adjustment plate 46A, and the piezoelectric element 42 is attached to the pressure adjustment plate 46A.

  The piezoelectric element 42 contracts or expands the volume in the pressure chamber 46 by changing the pressing force applied to the pressure adjusting plate 46A. That is, the ink stored in the ink tank 41 is ejected from the ink ejection nozzle 40 through the supply path 44 and the pressure chamber 46 by the vibration wave (pressure wave) of the ink generated by the change in the volume in the pressure chamber 46. It is like that.

  In FIG. 3, the recording head control unit 50 according to the present embodiment includes a controller 52 that controls the operation of each recording head 36 and a driving IC (Integrated) as a driving circuit provided corresponding to each of the recording heads 36. Circuit) 54.

  The controller 52 includes a CPU, a RAM, a ROM, and a signal generation circuit that generates various signals (not shown), and all drive ICs 54 provided corresponding to the respective recording heads 36 are connected. The controller 52 controls the operation of each recording head 36 by outputting a clock signal, a drive waveform designation signal, a latch signal, and a first drive waveform signal to a twelfth drive waveform signal to each drive IC 54. Yes.

  Even if a pulse voltage having the same waveform is applied to each piezoelectric element 42 due to variations in the characteristics of the piezoelectric elements 42 and manufacturing variations in the volume of the pressure chamber 46, the recording head 36 is ejected from each ejection mechanism 35. There may be variations in the droplet volume.

  Therefore, the recording head control unit 50 according to the present embodiment corrects the variation in the droplet amount obtained by measuring the variation in the droplet amount ejected from each ejection mechanism 35 when the recording head 36 is manufactured. Correction information for storing the image is stored in advance in a ROM (not shown), and the controller 52 designates a drive waveform signal to be used when recording the pixel based on the density of the pixel of the image indicated by the image data and the correction information. A drive waveform designation signal is output.

  Table 1 shows types of drive waveform signals used as the first to twelfth drive waveform signals.

  Since the selection signal is output as a bit signal, the types of the drive waveform signal and the selection signal are two types (1 bit), four types (2) depending on the number of bits representing the selection signal. Bit), 8 types (3 bits), 16 types (4 bits),..., But the present invention relates to a correction method, and the types of selection signals and drive waveform signals are not necessarily limited. Since it is not necessary to use a number corresponding to the number of bits, here, a case where 12 types of drive waveforms are used will be described.

  Preliminary drive waveform signals 1 to 3 shown in Table 1 are preliminary drive waveform signals selected when ink droplets are not ejected. In the present embodiment, the preliminary drive waveform signals 1 to 3 are applied to the piezoelectric element 42 without an ejection command, vibrated in a range where the ink liquid level (meniscus) of the nozzle portion is not ejected, and ink in the vicinity of the nozzle 40 is used. Stir the liquid to prevent nozzle clogging due to thickening of the ink.

  The large droplet driving waveform signal is a predetermined high concentration driving waveform (see FIG. 7A) for the piezoelectric element 42, and the medium droplet driving waveform signal and the low concentration driving waveform signal are These are drive waveform signals for generating a predetermined medium / low concentration drive waveform (see FIG. 8A) for the piezoelectric element 42. In addition, each of the drive waveform signals is preset in advance according to the manufacturing variation of each recording head 36 (details will be described later).

  FIG. 4 shows the configuration of the drive IC 54 according to the present embodiment.

  The drive IC 54 according to the present embodiment includes a shift register 56, a latch circuit 58, shift registers 60N1 to 60N12, a selector 62, a level shifter 64, and a switch element unit 66.

  The clock signal and the drive waveform designation signal output from the controller 52 are input to the shift register 56, and the latch signal is input to the latch circuit 58.

  In the following, in order to avoid complications, a case where a drive waveform is supplied to only one piezoelectric element 42 will be described, but the same applies to the other piezoelectric elements 42.

  The shift register 56 converts designation information designating a drive waveform to be applied to each piezoelectric element 42 indicated by the inputted drive waveform designation signal into parallel data and outputs the parallel data to the latch circuit 58.

  The latch circuit 58 latches (self-holds) the parallel data output from the shift register 56 according to the input of the latch signal.

  The selector 62 receives the first drive waveform signal to the sixteenth drive waveform signal from the controller 52 via the shift registers 60N1 to 60N12, and the designation information latched by the latch circuit 58 is input to the select terminal. Therefore, the selector 62 selects and outputs the drive waveform signal designated by the designation information from the first drive waveform signal to the twelfth drive waveform signal.

  The drive waveform signal output terminal of the selector 62 is connected to the level shifter 64, and the drive waveform signal output from the selector 62 is level-converted by the level shifter 64 and output. The level shifter 64 is supplied with power of a predetermined voltage level (18 V in the present embodiment) from a power source (not shown), and the level shifter 64 performs level conversion on the drive waveform signal designated by the drive waveform designation signal. To do.

  On the other hand, in the switch element section 66 according to the present embodiment, the drains of a P-channel MOS FET (hereinafter referred to as “PMOS”) 66A and an N-channel MOS FET (hereinafter referred to as “NMOS”) 66B are connected to each other. At the same time, the gates of PMOS 66A and NMOS 66B are connected.

  Here, the power of the voltage level V1 (18V in the present embodiment) from a variable power supply (not shown) is supplied to the source of the PMOS 66A in the switch element section 66, and the source of the NMOS 66B is grounded to the ground. It is considered a level. Further, one output terminal of the level shifter 64 is connected to each gate of the PMOS 66A and the NMOS 66B, and the drive waveform signal S which has been selected by the selector 62 and whose level has been converted by the level shifter 64 is input. .

  Accordingly, in the switch element unit 66, when the signal level of the drive waveform signal S input from the level shifter 64 is high, the PMOS 66A is turned off and the NMOS 66B is turned on, so that the voltage level of the output voltage is the ground level. Become a level. In contrast, when the signal level of the drive waveform signal S input from the level shifter 64 is low, the PMOS 66A is on and the NMOS 66B is off, so that the voltage level of the output voltage is the voltage level V1. And applied to the piezoelectric element 42.

  Here, FIG. 5 shows a change state of the drive waveform signal when passing through each part in the drive IC 54.

  FIG. 5A shows the drive waveform signal output from the selector 62. The drive waveform signal shown in the figure is level-converted to a predetermined voltage level by the level shifter 64 as shown in FIG.

  The drive waveform signal level-converted in this way is input to the switch element unit 66, and the output voltage of the switch element unit 66 is switched according to the voltage level of the drive waveform signal.

  That is, as shown in FIG. 5C, when the voltage level of the drive waveform signal is low level, the voltage of the voltage level V1 is applied to the piezoelectric element 42 via the switching element unit 66. When the voltage level of the drive waveform signal is high level, the voltage of the piezoelectric element 42 becomes the ground level.

  The voltage amplitude of the drive waveform is determined by the power supply voltage. Since the capacitance C is present in the piezoelectric element 42 and the on-resistance R is present in the PMOS 66A and NMOS 66B, the rise and fall of the binary digital drive waveform. , A slope determined by a time constant depending on the capacitance C and the on-resistance R is generated, and a time Ts is generated at the rise and fall of the voltage applied to the piezoelectric element 42.

  Based on the density of each pixel recorded by the recording head 36 in the image indicated by the image data, the controller 52 classifies the density level of the pixel as one of high density, medium density, low density, or no recording. A drive waveform designation signal for designating a drive waveform signal used when recording the pixel is output based on correction information stored in the ROM, and a clock signal, a latch signal, and a first drive waveform signal to a first drive waveform signal are output. 12 drive waveform signals are output. Note that if the density level of the pixel to be recorded is high, any of the large droplet drive waveform signals will be used. If the concentration is medium, any of the medium droplet drive waveform signals will be used. One of the waveform signals is output.

  In the drive IC 54, the designation information indicated by the inputted drive waveform designation signal is converted into parallel data, latched in the latch circuit 58, and continuously output to the selector 62.

  The selector 62 selects and outputs the drive waveform signal designated by the designation information from the first drive waveform signal to the twelfth drive waveform signal input via the shift registers 60N1 to 60N12.

  As a result, a plurality of types of large-drop drive waveforms, medium-drop drive waveforms, and small-drop drive waveforms prepared in accordance with manufacturing variations are used in accordance with the density of pixels recorded by each piezoelectric element 42 and manufacturing variations. Since the drive waveform is selected and applied, variations in ink droplets ejected from the ink ejection nozzles 40 of the ejection mechanisms 35 can be suppressed, and a good image can be recorded.

  Here, in the present embodiment, the pulses constituting the drive waveform of the voltage applied to the piezoelectric element 42 are the first steps for expanding the pressure chamber 46 (the drive shown in FIGS. 7A and 8A). Corresponding to the falling portion of the waveform), the second step of maintaining the pressure chamber 46 in an expanded state (corresponding to the low level portion of the drive waveform shown in FIGS. 7A and 8A), the pressure A third step of contracting the chamber 46 to the original position (corresponding to the rising portion of the drive waveform shown in FIGS. 7A and 8A) is included.

  In FIG. 6A, an ink liquid level (meniscus) 43 of the ink discharge nozzle 40 is schematically shown. When the pulse configured by the first to third steps described above is applied, a vibration wave is generated in the ink in the pressure chamber 46 due to a change in the volume of the pressure chamber 46. This vibration wave propagates in the pressure chamber 46, and as shown in the figure, the meniscus 43 of the ink discharge nozzle 40 is vibrated at the natural vibration period (also referred to as Helmholtz frequency) Tc of the ink liquid.

  FIG. 6B shows the relationship between the amplitude Y of the meniscus 43 shown in FIG. 6A and the natural vibration period Tc. Therefore, by adjusting the pulse interval and the application time, the vibration state of the meniscus 43 is controlled to eject a desired amount of ink droplets.

  By the way, in the present embodiment, in order to suppress variations in the volume of ink droplets ejected between the recording heads 36 and between the ejection mechanisms 35, relative to the ink droplet volume when the same drive waveform is applied. It is classified into three levels: a large high rank group, a relatively small low rank group, and a medium rank group that is an intermediate size.

  For this reason, three types of driving waveforms for large droplets, driving waveforms for medium droplets, and driving waveforms for small droplets are set for each rank.

  That is, for example, the large droplet driving waveform 1, the medium droplet driving waveform 1 and the small droplet driving waveform 1 are used as driving waveforms for the low rank group, and the large droplet driving waveform 2, the medium droplet driving waveform 2 and the small droplet are used. The driving waveform 2 for low rank group is used as the driving waveform for the low rank group, and the driving waveform 3 for large droplets, the driving waveform 3 for medium droplets, and the driving waveform 3 for small droplets are used as driving waveforms for the low rank group.

  Below, the setting method of each drive waveform which concerns on this Embodiment is demonstrated.

  FIG. 7A shows an example of a large droplet driving waveform applied to the piezoelectric element 42 when recording pixels in a high density portion. As shown in the figure, in the large droplet driving waveform, one pulse having a predetermined pulse width T1 is applied.

  In FIG. 7B, the recording head 36 according to the present embodiment is used, the bias voltage Vbias = 18V, the voltage amplitude V = 18V, the rise and fall time Ts = 1.0 μsec, and the pulse width T1 is changed. An example of a measurement result of the volume of ink droplets discharged from the ink discharge nozzles 40 of the discharge mechanism 35 of the high rank group, the medium rank group, and the low rank group is shown. As shown in the figure, the head of each rank shows a quadratic function characteristic, and the ink droplet volume is maximum at the pulse width T1 = 7.0 μsec.

  FIG. 7C shows the case where the recording head 36 according to the present embodiment is used and the pulse width T1 is changed with the bias voltage Vbias = 18 V, the voltage amplitude V = 18 V, and Ts = 1.0 μsec. 1 shows an example of the measurement result of the ink droplet speed ejected from the ejection mechanisms 35 of the high rank group, the middle rank group, and the low rank group. As shown in the figure, in each rank, the pulse width T1 = 6.5 μsec and the ink droplet speed is maximum.

  That is, the pulse width that maximizes the ink droplet volume is larger than the pulse width that maximizes the ink droplet velocity.

  Here, it is preferable to set a pulse width that maximizes the ink droplet volume for the large-droplet driving waveform (one pulse) in the low rank group, which has relatively low energy efficiency. In addition, it is preferable to determine the voltage amplitude V so that the ink droplet volume ejected using the pulse width set in this way becomes a desired droplet volume (drop volume according to the specification).

  Therefore, in the present embodiment, in order to prevent variation in the ink droplet volume, first, the pulse width T1 of the low rank group is set to a pulse width that maximizes the ink droplet volume (the pulse indicated by symbol C in the figure). Width, T1 = 7.0 μsec).

  The ink droplet velocity of the large droplets of the low rank group set in this way is 8.3 m / sec, as indicated by F in the figure (C), and the ink droplet volume is A in the figure (B). Is 8.0 pl as shown in FIG.

  Next, as the pulse width T1 of the high-rank group and the middle-rank group, a pulse width close to 8.0 pl indicated by A is applied.

  For example, as the pulse width T1 of the high rank group, by setting either the pulse width indicated by B in the figure or the pulse width indicated by D in the figure, variation in the ink droplet volume can be prevented. It turns out that it is possible.

  Here, in order to perform printing by ejecting ink droplets satisfactorily, it is necessary to suppress variation in ink droplet volume to suppress density unevenness, and also to reduce variation in ink droplet velocity to reduce ink droplet landing position. It is necessary to prevent image quality deterioration due to deviation.

  Therefore, in the present embodiment, as the pulse width T1 of the high rank group, a pulse width having a small ink droplet velocity difference from the ink droplet velocity F of the low rank group is set (the pulse width indicated by the symbol B in FIG. T1 = 4.5 μsec).

  Similarly, the pulse width T1 of the middle rank group is an ink drop with an ink drop velocity F of 5.5 μsec where the ink drop volume is close to the ink drop volume of the low rank group and 9.0 μsec. By applying a pulse width having a smaller speed difference, T1 = 5.5 μsec can be set.

  FIG. 8A shows an example of a medium / small droplet driving waveform applied to the piezoelectric element 42 when recording pixels in the medium density portion and the low density portion. As shown in the figure, in the medium / small droplet driving waveform, two pulses P1 and P2 having different pulse widths are applied.

  The pulse width T1 of the first pulse P1 is about ½ of the natural vibration period Tc of the vibration wave that propagates through the ink stored in the pressure chamber 46 due to the increase or decrease of the volume of the pressure chamber 46. . As a result, when the pulse P1 is applied to the piezoelectric element 42, the pressure chamber 46 contracts at a timing that resonates with the period in which the ink flow enters and exits the pressure chamber 46 due to the expansion of the pressure chamber 46. It is discharged from the nozzle 40.

  On the other hand, the pulse width T3 of the second pulse P2 is not less than the above-described fall time Ts and not more than 1/4 of the natural vibration period Tc of the ink liquid. As a result, when the non-ejection pulses P1 and P6 are applied, the pressure chamber 46 contracts at a timing that does not resonate with the period in which the ink flow enters and exits the pressure chamber 46 due to the expansion of the pressure chamber 46. The ink is drawn into the pressure chamber 46 and is not discharged from the ink discharge nozzle 40.

  By applying these two pulses P1 and P2 in order at intervals of a predetermined interval T2, when the pulse P1 for ejecting ink droplets is applied, the volume of the pressure chamber 46 changes to cause the ink ejection nozzle 40 to change. One ink droplet is ejected. However, since the pulse P2 that draws the ink droplet is applied after the interval T2 has elapsed, a part of the ejected ink droplet is drawn into the pressure chamber 46 and only one pulse P1 is applied. The volume of ink droplets ejected is smaller than that of.

  In FIG. 8B, the recording head 36 according to the present embodiment is used, the bias voltage Vbias = 18V, the voltage amplitude V = 18V, Ts = 1.0 μsec, T1 = 6.5 μsec, and the interval T2 is changed. An example of the measurement result of the volume of ink droplets ejected from the ink ejection nozzle 40 is shown. However, T3 is also changed according to the value of T2 so that T2 + T3 = 5.5 μsec. As shown in the figure, the ink droplet volume changes substantially linearly with respect to the interval T2.

  First, assuming that the desired ink droplet volume of the medium droplet is 4 pl (volume indicated by H in the figure), the interval T2 of the medium droplet driving waveform is T2 = 3.6 μsec for the low rank group and T2 for the medium rank group. = 2.8 μsec, and the high rank group can be set as T2 = 2.4 μsec.

  If the desired ink droplet volume of the small droplet is 2 pl (the volume indicated by I in the figure), the droplet driving waveform interval T2 is T2 = 2.0 μsec for the low rank group and T2 for the medium rank group. = 1.7 μsec and the high rank group can be set as T2 = 1.5 μsec.

  Here, Table 2 shows the parameters of each drive waveform and the volume and velocity of the ejected ink droplet when the variation in the ink droplet volume between the recording heads 36 and between the ejection mechanisms 35 is not corrected. In the figure, the parameters of each drive waveform and the volume and speed of the ejected ink droplet when the variation in the ink droplet volume between the recording heads 36 and between the ejection mechanisms 35 are corrected are shown.

  Tables 4 and 12 shown in parentheses in the column of drive waveform types in Tables 2 and 3 indicate the types of drive waveform signals in Table 1 to which the respective drive waveform types correspond. In addition, a portion indicated by a thick frame in Table 3 is a portion changed in order to correct the ink droplet volume.

  FIG. 9A is a graph showing the ink droplet volume without variation correction shown in Table 2 and the ink droplet volume with variation correction shown in Table 3. As shown in the figure, by setting the drive waveform by the above-described method, variations in ink droplet volume between the recording heads 36 and between the ejection mechanisms 35 are eliminated.

  FIG. 9B is a graph showing the ink droplet velocity without variation correction shown in Table 2 and the ink droplet velocity with variation correction shown in Table 3. As shown in the figure, when the drive waveform is set by the above-described method, the ink droplet speed remains varied between the recording heads 36 and between the ejection mechanisms 35.

  Therefore, as shown in FIG. 10, in this embodiment, in order to correct the landing position deviation due to the variation in the ink droplet velocity, the ink droplets land on the recording paper P after being ejected from the ink ejection nozzle 40. The landing time difference (landing time difference) T5 required for the above is derived in accordance with the ink droplet speed variation ΔV, and the timing for applying the drive waveform is adjusted by the landing time difference T5.

As shown in FIG. 11, the ink droplet velocity Vd, the variation of the ink droplet velocity ΔV, the distance between the ink ejection nozzle 40 and the recording paper P is the head paper distance d (m), the scanning direction resolution is n (dpi), If the ejection frequency is f (kHz), the ejection cycle is T0 = 1000 / f (μsec), and the scan speed is Vs = 25.4 × f / n (m / sec), the landing time difference T5 (sec) due to variations in ink droplet speed is It is expressed by the following (1).
Landing time difference T5 = [d / (Vd ± ΔV)] − d / Vd (1)
Table 4 shows that the distance between head papers d = 1.5e−3 (m), the scanning direction resolution n = 1200 (dpi), the ejection frequency f = 18 (kHz), and the ejection cycle T0 = 55.6 (μsec). The landing time difference T5 derived according to the ink droplet velocity when the drive waveform after the ink droplet volume correction shown in Table 3 is used is shown.

  As shown in Table 4, the ink droplet velocity Vd when the drive waveform having the smallest ink droplet velocity is applied as a reference and the drive waveform having the smallest ink droplet velocity is applied among the drive waveforms having the same ink droplet size. The landing time difference T5 is derived using the variation ΔV with respect to. Thereby, the landing position deviation between the drive waveforms having the same ink droplet size is eliminated.

  The ink droplet velocity Vd needs to be a velocity that does not disturb the shape of the droplet after landing according to the scan velocity Vs. Further, in order to prevent occurrence of landing position deviation due to external factors such as wind, it is preferable to set the speed to 5 m / sec or more regardless of the scanning speed.

  As described above in detail, according to the present embodiment, the pressure chamber 46 in which the ink discharge nozzle 40 is provided and the liquid is accommodated therein, and the piezoelectric driven by applying a binary digital drive waveform. Ink accommodated in a pressure chamber 46 has a plurality of sets of ejection mechanisms each including an element 42, and a pulse corresponding to image data is applied to the piezoelectric elements 42 of each ejection mechanism to drive the piezoelectric elements 42. When an image is recorded by applying a vibration wave to the liquid and ejecting droplets from the ink ejection nozzle 40, each ejection mechanism is divided into a high-rank group corresponding to the droplet volume ejected by the same pulse signal. When a pulse is applied to the piezoelectric element 42 for a low rank group including a discharge mechanism having the smallest droplet volume, which is classified into either a rank group or a low rank group. Is set in advance as the pulse width of one pulse signal (large droplet drive waveform), and when the large droplet drive waveform is applied to the piezoelectric element 42 for another group of ejection mechanisms. A large droplet is previously driven with a pulse width that is the same as the maximum droplet volume of the discharge mechanism of the low-rank group and smaller than the pulse width that maximizes the discharged droplet volume. Since the pulse width of the waveform is set and when a large droplet driving waveform is applied to the piezoelectric element 42, each ejection mechanism applies a preset pulse width to each classified group. The variation in the ink droplet volume between the heads and in the ejection mechanism in the head can be corrected only by changing in the time direction without changing the drive waveform in the voltage direction.

  In addition, as the pulse width of the low rank group including the ejection mechanism with the smallest ink droplet volume, the pulse width that maximizes the ink droplet volume is applied, and the ink droplet volume of the ejection mechanism of the high rank group and the middle rank group is low. Since it is set so as to match the ink droplet volume of the discharge mechanism of the rank group, the ink droplet volumes of the discharge mechanisms of all ranks can be matched with ease and accuracy.

  Furthermore, paying attention to the difference between the characteristics of the ink droplet volume and the ink droplet velocity with respect to the pulse width, the pulse width of the high rank group and the middle rank group is smaller than the pulse width that maximizes the ink droplet volume. Therefore, it is possible to prevent an increase in ink droplet speed difference due to correction of variation in ink droplet volume.

  In the present embodiment, correction in the case where there is a variation only in the efficiency of the piezoelectric element has been described. However, the present invention is not limited to this, and the case where there is a variation in the natural vibration period Tc of the ink. Also, the drive waveform can be set by the same method.

  For example, FIG. 12 shows ink drop volume characteristics (FIG. 12A) and ink drop velocity characteristics (FIG. 13) when the natural vibration period Tc of the high rank group is smaller than the natural vibration period Tc of the low rank group. (B)) is shown respectively. As shown in the figure, by setting the drive waveform by the same method as in the above embodiment, the variation in the ink droplet volume can be corrected well.

  FIG. 13 also shows ink drop volume characteristics (FIG. 13A) and ink drop velocity characteristics (FIG. 13) when the natural vibration period Tc of the high rank group is larger than the natural vibration period Tc of the low rank group. (B)) is shown respectively. As shown in the figure, by setting the drive waveform by the same method as in the above embodiment, the variation in the ink droplet volume can be corrected well.

  Therefore, even when the ink droplet volume variation between the recording heads 36 is corrected, the ink droplet volume variation can be corrected well.

  Note that the configuration of the printer 10 according to the present embodiment (see FIGS. 1 and 2) and the configuration of the recording head control unit 50 (see FIGS. 3 and 4) are examples, and do not depart from the gist of the present invention. Needless to say, it can be appropriately changed.

  Further, the measured values and the like (see FIGS. 7 to 9, 12 and 13, and Tables 1 to 4) are also examples, and each value is an actual recording head specification or a natural vibration period in the flow path of the liquid to be ejected. It can set suitably according to etc.

  Further, although the printer 10 according to the present embodiment records an image (including characters) on a recording medium, the droplet discharge device of the present invention is not limited to this. That is, the recording medium is not limited to the recording paper P, and the liquid to be discharged is not limited to ink. For example, the present invention can also be applied to other droplet discharge recording apparatuses such as a pattern forming apparatus that discharges droplets onto a sheet-like substrate for pattern formation of a semiconductor or a liquid crystal display.

1 is a schematic diagram illustrating a configuration of an FWA type inkjet printer according to an embodiment. FIG. 2 is a cross-sectional view illustrating a configuration of a recording head according to an embodiment. FIG. 2 is a block diagram illustrating a configuration of a recording head control unit according to an embodiment. It is a block diagram (partial circuit diagram) showing a detailed configuration of a drive IC according to an embodiment. It is a wave form diagram which shows the drive waveform signal in each part of the drive IC which concerns on embodiment. (A) is an enlarged view showing the vibration of the meniscus of the ink discharge nozzle, and (B) is a waveform diagram showing the relationship between the amplitude and period of the meniscus by the vibration wave. (A) is a wave form diagram which shows the drive waveform for large drops which concerns on embodiment, (B) is a graph which shows the measurement result of the ink drop volume discharged from the ink discharge nozzle when changing the pulse width T1. (C) is a graph showing the measurement result of the ink droplet velocity ejected from the ink ejection nozzle when the pulse width T1 is changed. (A) is a wave form diagram which shows the drive waveform for medium droplets / small droplets according to the embodiment, and (B) shows the measurement result of the volume of ink droplets ejected from the ink ejection nozzle when the interval T2 is changed. (C) is a graph showing the measurement result of the ink droplet velocity ejected from the ink ejection nozzle when the interval T2 is changed. (A) is a graph showing ink droplet volumes before and after variation correction based on Tables 2 and 3, and (B) is a graph showing ink droplet speeds before and after variation correction based on Tables 2 and 3. It is. It is explanatory drawing regarding the correction | amendment of the dispersion | variation in ink droplet speed. It is a figure which shows the relationship between an ink discharge nozzle and a recording paper. FIG. 6 is a graph showing characteristics when the natural vibration period Tc of the high rank group is smaller than the natural vibration period Tc of the low rank group, FIG. It is a graph which shows a characteristic. FIG. 6 is a graph showing characteristics when the natural vibration period Tc of the high rank group is larger than the natural vibration period Tc of the low rank group, FIG. It is a graph which shows a characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Printer 35 Discharge mechanism 36 Recording head 40 Ink discharge nozzle 42 Piezoelectric element 43 Meniscus 46 Pressure chamber 50 Recording head control part 52 Controller 66 Switch element part

Claims (11)

A pressure chamber provided with a discharge port and containing liquid therein, and a piezoelectric element that is driven by applying a pulse signal that is a binary digital drive waveform. The pulse signal is transmitted to the piezoelectric element. A plurality of ejection mechanisms for applying a vibration wave to the liquid contained in the pressure chamber by applying and driving the piezoelectric element to eject droplets from the ejection port, and the pulse width of each ejection mechanism−liquid A method for driving a droplet discharge recording head exhibiting a quadratic function characteristic in which the droplet volume characteristic has a maximum point,
Each discharge mechanism is classified into at least two types of groups according to the difference in pulse width-droplet volume characteristics of each discharge mechanism due to the difference in electrical conversion efficiency of the piezoelectric elements constituting each discharge mechanism,
When setting the pulse width for discharging one pulse droplet so that the volume of droplets discharged by applying one pulse is equal between the groups for each group,
The liquid is characterized in that it is set so that the pulse width of the group on the higher rank side is relatively narrower than the pulse width of the group on the lower rank side including the ejection mechanism having relatively poor electrical conversion efficiency. A method for driving a droplet discharge recording head. 2. The droplet discharge according to claim 1, wherein the relatively low-rank group has a pulse width at which the droplet volume becomes a maximum point as a pulse signal for discharging one pulse droplet. Driving method of the recording head.   3. The method of driving a droplet discharge recording head according to claim 2, wherein a pulse width at which the droplet volume becomes a maximum point is ½ times the natural vibration period of the liquid flow in the liquid flow path. A pressure chamber provided with a discharge port and containing liquid therein, and a piezoelectric element that is driven by applying a pulse signal that is a binary digital drive waveform. The pulse signal is transmitted to the piezoelectric element. This is a method for driving a droplet discharge recording head having a plurality of discharge mechanisms for applying a vibration wave to the liquid contained in the pressure chamber by applying and driving the piezoelectric element to discharge droplets from the discharge port. And
Each of the ejection mechanisms is classified into a plurality of groups corresponding to the droplet volume ejected when a pulse signal having the same pulse width is applied to each piezoelectric element,
When setting the pulse width of one pulse for each group so that the droplet volume when one pulse is applied becomes a predetermined droplet volume,
A method for driving a droplet discharge recording head, wherein the pulse width of another group is set to be narrower than the pulse width of a low rank group including the discharge mechanism having the smallest droplet volume.   The pulse width of the low rank group including the discharge mechanism having the smallest droplet volume is set to a pulse width that maximizes the droplet volume when one pulse is applied to the piezoelectric element for the low rank group. 5. A method of driving a droplet discharge recording head according to claim 4.   The liquid according to any one of claims 1 to 5, wherein the application timing of the one pulse is delayed for a group having a higher droplet velocity in accordance with a difference in droplet velocity between the groups. A method for driving a droplet discharge recording head.   2. When droplets are ejected by applying two pulses to the piezoelectric element at a predetermined interval, variation in droplet volume is corrected by varying the interval for each group. The method for driving a droplet discharge recording head according to any one of claims 1 to 6.   8. The method of driving a droplet discharge recording head according to claim 7, wherein the interval is varied so that the sum of the interval and the pulse width of the second pulse is constant.   9. The droplet discharge according to claim 1, comprising a plurality of the droplet discharge recording heads, and correcting variations in droplet discharge characteristics between the droplet discharge recording heads. Driving method of the recording head.   The pulse has a first step of expanding the pressure chamber by falling from the bias voltage, a second step of maintaining the voltage constant and expanding the pressure chamber, and a pressure chamber by rising to the bias voltage. The method for driving a droplet discharge recording head according to any one of claims 1 to 9, further comprising a third step of contracting to an original position. A pressure chamber provided with a discharge port and containing liquid therein, and a piezoelectric element that is driven by applying a pulse signal that is a binary digital drive waveform. The pulse signal is transmitted to the piezoelectric element. A droplet discharge recording head having a plurality of discharge mechanisms for applying a vibration wave to the liquid accommodated in the pressure chamber by applying and driving the piezoelectric element to discharge droplets from the discharge port;
Storage means for storing classification data classified into a plurality of groups according to droplet volumes ejected when each ejection mechanism applies a pulse signal of the same pulse width to each piezoelectric element;
The droplet volume when one pulse is applied is set to a predetermined droplet volume, and the pulse width of the other group is set to be narrower than the pulse width of the low rank group including the discharge mechanism having the smallest droplet volume. Table
Control means for applying a preset pulse width of the table to a group into which each ejection mechanism is classified when one pulse is applied to the piezoelectric element;
A droplet discharge recording apparatus comprising:

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