JP2012106353A - Waveform generator and inkjet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain stable ejection in continuous ejection even in the condition that a dissolved gas amount in a liquid does not fall.SOLUTION: This waveform generator generates a driving waveform to be supplied to actuators of an inkjet head including nozzles which eject liquid droplets, liquid chambers which communicate with the nozzles and the actuators which pressurize the liquid in the liquid chambers. In the waveform generator generating the driving waveform, ejection waveform elements which make the nozzles eject the liquid droplets and n (n≥3) pieces of which excite resonance of the inkjet head are disposed at equal intervals, and a non-ejection waveform element which does not make the liquid droplet ejected is provided between the m-th (2≤m<n) ejection waveform element and the m+1-th ejection waveform element.

Description

  The present invention relates to a waveform generation device and an ink jet recording apparatus, and more particularly to an ink jet image forming technique for continuously ejecting ink.

  In an ink jet recording apparatus that forms a desired image on a recording medium using an ink jet method, a technique for expressing gradation by forming dots of different sizes by controlling the number of ink droplets to be ejected is known. ing. In such an apparatus, it is necessary to stably and continuously discharge a certain amount of ink.

  As a method for maintaining accurate discharge, a technique that suppresses the influence of the previous discharge on the next discharge by adding a drive waveform that suppresses reverberation to the actuator after discharging is known, focusing on meniscus vibration. (Patent Documents 1 and 2). In addition, a technique is known that suppresses the occurrence of unintentional discharge such as satellites and mist by controlling how the liquid column is cut during discharge (Patent Document 3).

  As described above, various drive waveforms have been proposed for driving the actuator.

Japanese Patent No. 2969570 JP 2001-18388 A JP 2009-274433 A

  All of these conventional techniques pay attention to the movement of the meniscus of the nozzle and take measures to bring it closer to a desired state. However, in the control of the meniscus state, the state inside the head cannot be sufficiently controlled.

  For example, the presence of bubbles in the head or the growth of bubbles may affect the ejection performance. In such a case, it is effective to degas the ink for stable ejection. However, such factors cannot be controlled well simply by controlling the meniscus state.

  SUMMARY An advantage of some aspects of the invention is that it proposes a suitable driving waveform and provides a waveform generating apparatus and an ink jet recording apparatus capable of maintaining stable ejection.

  In order to achieve the above object, the waveform generating apparatus according to claim 1 is an inkjet including a nozzle that discharges droplets, a liquid chamber that communicates with the nozzle, and an actuator that pressurizes the liquid in the liquid chamber. In a waveform generation device that generates a drive waveform to be supplied to an actuator of a head, there are n (n ≧ 3) discharge waveform elements that excite the resonance of the inkjet head, which are discharge waveform elements that discharge droplets from the nozzles. Are arranged at equal intervals, and a drive waveform having a non-ejection waveform element that does not eject droplets between the mth (2 ≦ m <n) ejection waveform element and the m + 1th ejection waveform element from the front is generated. It is characterized by doing.

  According to the first aspect of the present invention, n (n ≧ 3) ejection waveform elements that eject droplets from the nozzles and excite resonance of the inkjet head are arranged at equal intervals, A drive waveform having a non-ejection waveform element that does not eject droplets between the m-th (2 ≦ m <n) ejection waveform element and the (m + 1) th ejection waveform element from the front is generated. As a result, the resonance of the inkjet head is excited and droplets are continuously ejected from the nozzle, and the continuous firing can be performed while suppressing the increase in pressure amplitude inside the inkjet head. The manifestation of gas due to pressure is suppressed, and stable ejection can be maintained.

  According to a second aspect of the present invention, in the waveform generating device according to the first aspect, the n ejection waveform elements are waveform elements having the same time width.

  As a result, it is possible to appropriately spray n droplets from the nozzle.

  According to a third aspect of the present invention, in the waveform generating device according to the first or second aspect, an interval between the n ejection waveform elements is in a range of 90 to 110% of a resonance period of the inkjet head. And

  As a result, it is possible to appropriately spray n droplets from the nozzle. Note that the resonance period (Helmholtz natural vibration period) of the ink jet head refers to the natural period of the entire vibration system determined from the ink flow path system, ink (acoustic element), dimensions, materials, physical property values, and the like of the pressure generating element.

  According to a fourth aspect of the present invention, in the waveform generating device according to any one of the first to third aspects, the ejection waveform element is a rectangular wave or a trapezoidal wave.

  Thereby, a droplet can be appropriately discharged from a nozzle.

  According to a fifth aspect of the present invention, in the waveform generation device according to any one of the first to fourth aspects, the non-ejection waveform element is a rectangular wave or a trapezoidal wave.

  Thereby, the pressure inside an inkjet head can be controlled appropriately.

  According to a sixth aspect of the present invention, in the waveform generating device according to any one of the first to fifth aspects, the width of the non-ejection waveform element is equal to or less than the width of the ejection waveform element.

  Thereby, the pressure inside an inkjet head can be controlled appropriately.

  The waveform generation device according to any one of claims 1 to 6, wherein the amplitude of the non-ejection waveform element is the amplitude of the mth ejection waveform element from the front and the amplitude from the front. It is below the average with the amplitude of the m + 1th discharge waveform element.

  Thereby, the pressure inside an inkjet head can be controlled appropriately.

  In order to achieve the above object, an ink jet recording apparatus according to an eighth aspect includes a waveform generating apparatus according to any one of the first to seventh aspects, a nozzle that ejects droplets, and a liquid that communicates with the nozzle. An inkjet head including a chamber and an actuator that pressurizes the liquid in the liquid chamber, driving means for supplying the generated driving waveform to the actuator and causing droplets to be ejected n times from the nozzle, a recording object, and the object And a moving means for relatively moving the inkjet head.

  According to the invention described in claim 8, the discharge waveform elements for discharging droplets from the nozzles, wherein n (n ≧ 3) discharge waveform elements for exciting the resonance of the inkjet head are arranged at equal intervals, A drive waveform having a non-ejection waveform element that does not cause droplets to be ejected between the mth (2 ≦ m <n) ejection waveform element and the m + 1th ejection waveform element from the front is generated and supplied to the actuator. Droplets are sprayed n times from the nozzle. As a result, continuous increase in pressure can be performed while suppressing an increase in pressure amplitude inside the ink jet head, so that gas can be prevented from appearing due to negative pressure inside the ink jet head, and stable ejection can be maintained. it can.

  According to the present invention, the negative pressure state inside the inkjet head is suppressed, and stable ejection can be maintained.

1 is a block diagram of an inkjet discharge apparatus according to an embodiment of the present invention. Sectional drawing which shows the structural example of the inkjet head shown in FIG. The figure which shows the relationship between the drive signal at the time of 1 drop discharge, and a pressure The figure which shows the relationship between the drive signal at the time of the conventional 4 droplet discharge, and a pressure The figure which shows the relationship between the drive signal at the time of 4 droplet discharge of this embodiment, and a pressure. External perspective view of ink jet recording apparatus Explanatory drawing schematically showing the recording medium conveyance path Plane perspective view showing an example of an arrangement form of an ink jet head and a curing light source Block diagram showing the configuration of the ink supply system Block diagram showing the configuration of an inkjet recording apparatus

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

[Description of inkjet discharge device]
FIG. 1 is a block diagram of an inkjet discharge apparatus according to an embodiment of the present invention. The inkjet discharge apparatus 100 shown in this example includes an inkjet head 24 that discharges droplet-like liquid (droplet) by an inkjet method, and a drive apparatus that operates the inkjet head 24 by supplying a predetermined drive signal to the inkjet head 24. 140.

  The inkjet head 24 is provided with a piezoelectric actuator 160 that serves as a pressure source when ejecting droplets. The piezoelectric actuator 160 operates in accordance with a drive signal supplied from the driving device 140 to eject droplets. The piezoelectric method is applied. Although details will be described later (see FIG. 2), the ink jet head 24 communicates with a nozzle serving as a droplet discharge port, a pressure chamber pressurized by a piezoelectric actuator 160, and the pressure chamber. Configurations such as a liquid flow path are provided.

  The driving device 140 includes a waveform generation unit 142, a signal selection unit 146, and a head driving circuit 128.

  The waveform generation unit 142 generates a reference drive waveform for driving the piezoelectric actuator 160. The head driving circuit 128 amplifies the power of the reference driving waveform input from the waveform generating unit 142.

  Further, the signal selection unit 146 turns on / off the drive signal after power amplification output from the head drive circuit 128 based on the ejection data, and selects presence / absence of a droplet to be ejected. When ejecting, the signal output from the head drive circuit 128 is supplied to the piezoelectric actuator 160. The signal selection unit 146 may be configured to control the droplet size by selecting the number of ejection waveform elements of the drive signal composed of a plurality of ejection waveform elements.

  Note that the inkjet head 24 and the drive device 140 may be configured separately and connected using a wiring member such as a flexible substrate, or the inkjet head 24 and the drive device 140 may be integrated.

[Configuration of inkjet head]
Next, a structural example of the inkjet head 24 shown in FIG. 1 will be described.

  FIG. 2 is a cross-sectional view showing an example of the three-dimensional structure of the ink jet head 24, and illustrates one-channel droplet discharge elements serving as recording element units.

  The ink jet head 24 shown in the figure operates the piezoelectric element 151 provided on the ceiling surface of the pressure chamber 150 to pressurize the liquid in the pressure chamber 150 and discharge the liquid droplets from the nozzle 152 communicating with the pressure chamber 150. It is configured to let you. When liquid droplets are ejected from the nozzle 152, the liquid flows from a tank (not shown) serving as a liquid supply source to the pressure chamber 150 via the common flow path 154 via a supply port 153 communicating with the pressure chamber 150. Filled.

  2 includes a nozzle plate 156 in which a nozzle 152 is formed on a nozzle surface 155, a flow path plate 157 in which a flow path such as a pressure chamber 150, a supply port 153, and a common flow path 154 is formed. It has a laminated structure. The nozzle plate 156 constitutes the nozzle surface 155 of the inkjet head 24, and a plurality of nozzles 152 communicating with the respective pressure chambers 150 are arranged in a predetermined arrangement pattern.

  The flow path plate 157 constitutes a side wall of the pressure chamber 150 and a flow in which a supply port 153 is formed as a constricted portion (most narrowed portion) of an individual supply path that guides liquid from the common flow channel 154 to the pressure chamber 150. It is a path forming member. For convenience of explanation, although shown in FIG. 2 in a simplified manner, the flow path plate 157 has a structure in which one or a plurality of substrates are stacked. The nozzle plate 156 and the flow path plate 157 can be processed into a required shape by a semiconductor manufacturing process using silicon as a material.

  A diaphragm 158 constituting a part of the pressure chamber 150 (the ceiling surface in FIG. 2) includes an upper electrode (individual electrode) 162 and a lower electrode 164, and a piezoelectric element is interposed between the upper electrode 162 and the lower electrode 164. A piezoelectric element (piezo element) 151 having a structure in which a body 166 is sandwiched is joined. When the diaphragm 158 is formed of a metal thin film or a metal oxide film, it functions as a common electrode corresponding to the lower electrode 164 of the piezoelectric element 151. In the aspect in which the diaphragm is formed of a non-conductive material such as resin, a lower electrode layer made of a conductive material such as metal is formed on the surface of the diaphragm member.

  By applying a driving voltage to the upper electrode 162, the piezoelectric element 151 is deformed and the diaphragm 158 is deformed to change the volume of the pressure chamber 150, and a droplet is ejected from the nozzle 152 due to the pressure change accompanying this.

  The piezoelectric actuator 160 shown in FIG. 1 includes the piezoelectric element 151 and the diaphragm 158 shown in FIG. 2, and serves as a pressure generation source that generates a liquid discharge pressure in accordance with a drive signal. Note that the piezoelectric actuator 160 may have a mode in which the vibration plate 158 illustrated in FIG. 2 is omitted (for example, a bimorph structure in which two piezoelectric elements are stacked).

[Drive signal and internal pressure]
Here, the relationship between the drive signal for driving the piezoelectric actuator 160 and the pressure inside the pressure chamber 150 will be described.

  FIG. 3A is a diagram schematically showing one ejection cycle of the drive signal 200 during one drop ejection, where the horizontal axis represents time (μs) and the vertical axis represents voltage (relative value). As shown in the figure, the drive signal 200 has an ejection pulse (ejection waveform element) 201 that is a rectangular wave having a pulse width of 5.4 μs and an amplitude (voltage) of a predetermined value. The drive signal 200 is generated by the waveform generation unit 142, power amplified by the head drive circuit 128, and then supplied to the piezoelectric actuator 160.

  The ejection pulse 201 is a waveform element for operating the piezoelectric actuator 160 to eject a predetermined amount of droplets from the nozzle 152. The rising portion (0 V → predetermined voltage) of the ejection pulse 201 shown in this example operates the piezoelectric actuator 160 so as to draw the meniscus into the nozzle (pulling operation), and the falling portion (predetermined voltage → 0 V) causes the meniscus to nozzle. The piezoelectric actuator 160 is operated so as to push out to the outside of 152 (pushing operation). The ejection pulse 201 may be a trapezoidal wave.

  FIG. 3B shows the pressure (relative value) inside the pressure chamber 150 when the drive signal 200 (the signal after power amplification thereof) is applied to the piezoelectric actuator 160.

  As shown in FIG. 3B, when the ejection pulse 201 rises, the piezoelectric actuator 160 is pulled, so that the pressure inside the pressure chamber 150 becomes negative. Thereafter, the pressure inside the pressure chamber 150 oscillates in accordance with the resonance period obtained from the structure of the inkjet head 24 shown in FIG. When the ejection pulse 201 falls in synchronization with this vibration, the piezoelectric actuator 160 is pushed and the pressure greatly fluctuates in the positive direction.

  FIG. 3C shows the ink flow velocity (relative value) at the nozzle 152 when the drive signal 200 is applied to the piezoelectric actuator 160. Here, the flow rate of ink from the nozzle 152 toward the inside of the pressure chamber 150 is represented as positive on the vertical axis, and the flow rate of ink from the nozzle 152 toward the outside of the pressure chamber 150 is represented as negative. As shown in the figure, the flow rate of the ink in the nozzle 152 changes according to the pressure fluctuation shown in FIG.

  FIG. 3D shows the ink meniscus position (relative value) obtained by integrating the ink flow velocity shown in FIG. In the figure, the position of the nozzle 152 is 0, the inside of the pressure chamber 150 is positive on the vertical axis, and the outside of the pressure chamber 150 is negative.

  Here, the amount of ink ejected by the drive signal 200 is considered to be substantially equivalent to the integral amount of one cycle of the ink flow velocity that varies with the application of the ejection pulse 201. Therefore, ink is ejected when the integral amount of one cycle becomes the negative minimum value in FIG.

  Next, the relationship between the driving signal at the time of conventional multi-drop ejection and the pressure inside the pressure chamber 150 will be described. Conventionally, when continuous ejection is performed at high speed, it is common to apply an ejection waveform that excites resonance of an inkjet head to an actuator a plurality of times at a substantially resonant period.

  FIG. 4A is a diagram schematically showing one ejection cycle of the driving signal 210 during the conventional four-drop ejection. This drive signal 210 has four ejection pulses 212-1 to 212-4. Each ejection pulse 212 is a rectangular wave having a pulse width of 4.4 μs and an amplitude of a predetermined voltage.

  Here, the four ejection pulses 212-1 to 212-4 all have the same amplitude, but may have different amplitudes. For example, in order to unite the droplets ejected by each ejection pulse in the air, it is conceivable to increase the amplitude later in time. As a result, the speed of the liquid droplet ejected later in time can be increased.

  The output period of the ejection pulse 212 is substantially equal to the resonance period (Helmholtz period TC) obtained from the structure of the inkjet head 24. Here, it is configured to output continuously at a period (interval) of 10 μs. The output period of the ejection pulse 212 may be 90% to 110% of the resonance period.

  Further, the pulse width of each ejection pulse 212 may be determined as appropriate. Further, the ejection pulse 212 may be a trapezoidal wave.

  After the drive signal 210 is amplified in the head drive circuit 128 and then supplied to the piezoelectric actuator 160, four droplets can be continuously discharged from the nozzle 152. When these four droplets are united in the air and land on the droplet ejection target, it is possible to form a dot having a size larger than that in the case of one droplet ejection on the droplet ejection target.

  4B and 4C show the pressure (relative value) in the pressure chamber 150 and the ink flow velocity (relative value) in the nozzle 152 when the drive signal 210 is applied to the piezoelectric actuator 160, respectively. Yes.

  As shown in FIG. 4B, when a plurality of ejection pulses are continuously applied, the pressure amplitude inside the pressure chamber 150 gradually increases.

  As described above, the amount of ink ejected by each ejection pulse 212 is equivalent to the integral amount of one cycle of fluctuations in the ink flow rate caused by the application of each ejection pulse 212. When this integration amount is a negative minimum value, ink is ejected.

  However, when the pressure amplitude exceeds a certain value, a problem occurs that gas (air) enters from the nozzle 152 and ink cannot be ejected.

  In order to avoid such a problem, a certain time during which no ejection is performed is provided in the drive signal at the time of multi-drop ejection, while waiting for the pressure inside the pressure chamber 150 to decay, or after ink ejection Measures such as outputting an attenuation pulse for attenuating the pressure fluctuation in the pressure chamber 150 are required.

[Driving signal of this embodiment]
Next, the drive signal according to the present embodiment will be described. FIG. 5A schematically shows one ejection cycle of the drive signal 220 supplied to the piezoelectric actuator 160 according to the present embodiment, and shows a drive signal for ejecting four drops. The drive signal 220 is generated by the waveform generation unit 142, power amplified by the head drive circuit 128, and then supplied to the piezoelectric actuator 160.

  As shown in the figure, this drive signal 220 has four ejection pulses 222-1 to 222-4 and one pressure suppression pulse 225.

  Each ejection pulse 222 is a rectangular wave having a pulse width of 4.4 μs and an amplitude of a predetermined voltage, and is configured to be continuously output at a period (interval) of 10 μs that is a resonance period of the inkjet head 24. As in the case of the ejection pulse 212 shown in FIG. 4A, the amplitude, output period, pulse width, and the like of the ejection pulse 222 may be determined as appropriate so that stable ejection can be performed stably.

  The pressure suppression pulse 225 is a rectangular wave having a pulse width of 3.2 μs and the same voltage as that of each ejection pulse 222, and the second ejection pulse from the front among the four ejection pulses 222-1 to 222-4. It is configured to be output between 222-2 and the third ejection pulse 222-3 from the front. The ejection pulse 222 and the pressure suppression pulse 225 may be trapezoidal waves.

  The four ejection pulses 222-1 to 222-4 can eject four droplets from the nozzle 152 in the same manner as the ejection pulses 212-1 to 212-4 of the drive signal 210 described above.

  On the other hand, the pressure suppression pulse 225 is not a waveform element that ejects ink from the nozzle 152 but a waveform element that suppresses an increase in pressure in the pressure chamber 150.

  The rising portion (0 V → predetermined voltage) of the pressure suppression pulse 225 operates the piezoelectric actuator 160 to pull the meniscus into the nozzle (pulling operation), and the falling portion (predetermined voltage → 0 V) causes the meniscus to be external to the nozzle 152. The piezoelectric actuator 160 is operated so as to be pushed out (pushing operation). As described above, the operation of the piezoelectric actuator 160 by applying the pressure suppression pulse 225 is the same as that of the ejection pulse 222. However, output during the ejection pulse 222 suppresses an increase in pressure in the pressure chamber 150 when ink is ejected continuously.

  The amplitude of the pressure suppression pulse 225 is preferably equal to or less than the average value of the amplitudes of the ejection pulses 222 (here, ejection pulses 222-2 and 222-3) before and after that. Further, the pulse width of the pressure suppression pulse 225 is preferably equal to or smaller than the width of each ejection pulse 222. The pressure suppression effect of the pressure suppression pulse 225 is maximized when the amplitude and pulse width are at the upper limit, and decreases as the amplitude and pulse width decrease. Therefore, an appropriate amplitude and pulse width may be determined in consideration of the volume, velocity, and ejection quality of the ejected droplet.

  FIG. 5B shows the pressure (relative value) inside the pressure chamber 150 when the drive signal 220 is applied to the piezoelectric actuator 160, and the scale of the vertical axis is the same as FIG. 4B. FIG. 5C shows the flow rate (relative value) of the ink in the nozzle 152, and the scale of the vertical axis is the same as that in FIG. 4C. As can be seen from these figures, the pressure amplitude and the ink flow rate do not increase even though the ejection pulses 222-1 to 222-4 are continuously output.

  Thus, by using the pressure suppression pulse 225, the state of the pressure in the pressure chamber 150 at the time of ink ejection can be controlled to a state where the negative pressure is small or a negative pressure period equal to or greater than a predetermined value is short. .

  Here, by optimizing the shape (pulse width, amplitude, etc.) of the pressure suppression pulse 225, the center value of the waveform of the ink flow rate in the resonance period, that is, the average value of the waveform shape of the ink flow rate can be changed. . As a result, the integral amount of the ink flow velocity in the resonance period can be set to a negative value, and control can be performed so that ink is ejected continuously.

  As described above, by outputting a pressure suppression pulse having substantially the same shape as the ejection pulse between the mth ejection pulse and the (m + 1) th ejection pulse, the pressure amplitude in the pressure chamber does not tend to expand. In addition, ink can be discharged continuously.

  This makes it possible to suppress the manifestation of dissolved gas in the ink jet head and the growth of gas already present in the ink jet head due to the negative pressure in the pressure chamber. Therefore, a desired pressure does not occur due to the gas present in the ink jet head even though the actuator is driven, and the possibility of defective ejection or non-ejection is reduced, and stable ejection becomes possible. In this way, it is possible to stabilize ejection using the pressure suppression pulse without degassing the ink.

  In the drive signal 220 of the present embodiment, the pressure between the second ejection pulse 222-2 from the front and the third ejection pulse 222-3 from the front among the four consecutive ejection pulses 222-1 to 222-4. Although the suppression pulse 225 is inserted, the position of the pressure suppression pulse 225 is not limited to this position. That is, among n (n ≧ 3) consecutive ejection pulses, a pressure suppression pulse is inserted between the mth (2 ≦ m <n) ejection pulse and the (m + 1) th ejection pulse from the front. (Superimposition) may be performed.

  Further, the pressure suppression pulse inserted in one cycle of the drive signal is not limited to one, and a plurality of pressure suppression pulses may be used. For example, in a driving waveform having six ejection pulses, the first pressure suppression pulse is inserted between the second ejection pulse and the third ejection pulse from the front, and the fourth ejection from the front. A second pressure suppression pulse may be inserted between the pulse and the fifth ejection pulse.

  The generation of the drive signal 220 in the waveform generation unit 142 may generate the discharge pulse and the pressure suppression pulse simultaneously by one pulse generator, or the discharge pulse train and the pressure suppression pulse generated by the two pulse generators later. You may superimpose. Further, it may be superimposed after power amplification by the head drive circuit 128.

<Overall configuration of inkjet recording apparatus>
FIG. 6 is an external perspective view of the ink jet recording apparatus according to the embodiment of the present invention. The ink jet recording apparatus 10 is a wide format printer that forms a color image on a recording medium 12 using ultraviolet curable ink (UV curable ink). A wide format printer is an apparatus suitable for recording a wide drawing range, such as a large poster or a commercial wall advertisement. Here, those corresponding to A3 Nobi or higher are called “wide format”.

  The ink jet recording apparatus 10 includes an apparatus main body 20 and support legs 22 that support the apparatus main body 20. The apparatus main body 20 includes a drop-on-demand type inkjet head 24 that ejects ink toward the recording medium (medium) 12, a platen 26 that supports the recording medium 12, and a guide mechanism as a head moving unit (scanning unit). 28 and a carriage 30 are provided.

  The guide mechanism 28 is disposed above the platen 26 so as to extend along a scanning direction (Y direction) perpendicular to the conveyance direction (X direction) of the recording medium 12 and parallel to the medium support surface of the platen 26. ing. The carriage 30 is supported so as to reciprocate in the Y direction along the guide mechanism 28. An ink jet head 24 is mounted on the carriage 30, and temporary curing light sources 32 </ b> A and 32 </ b> B that irradiate ink on the recording medium 12 with ultraviolet rays and main curing light sources 34 </ b> A and 34 </ b> B are mounted.

  The temporary curing light sources 32A and 32B are light sources that irradiate ultraviolet rays for temporarily curing the ink so that the adjacent droplets do not coalesce after the ink droplets ejected from the inkjet head 24 have landed on the recording medium 12. is there. The main curing light sources 34 </ b> A and 34 </ b> B are light sources that irradiate with ultraviolet rays for performing additional exposure after temporary curing and finally completely curing (main curing) the ink.

  The inkjet head 24, the temporary curing light sources 32 </ b> A and 32 </ b> B, and the main curing light sources 34 </ b> A and 34 </ b> B disposed on the carriage 30 move integrally with the carriage 30 along the guide mechanism 28. The reciprocating direction (Y direction) of the carriage 30 may be referred to as “main scanning direction”, and the transport direction of the recording medium 12 (X direction, hereinafter referred to as “media transport direction”) may be referred to as “sub-scanning direction”.

  As the recording medium 12, various media such as paper, non-woven fabric, vinyl chloride, synthetic chemical fiber, polyethylene, polyester, and tarpaulin can be used regardless of the material, regardless of permeable medium or non-permeable medium. it can. The recording medium 12 is fed from the back side of the apparatus in a roll paper state (see FIG. 7), and after printing, is wound up by a winding roller (not shown in FIG. 6, reference numeral 44 in FIG. 7) on the front side of the apparatus. . Ink droplets are ejected from the inkjet head 24 to the recording medium 12 conveyed on the platen 26, and the temporary curing light sources 32A and 32B and the main curing light sources 34A and 34B are applied to the ink droplets attached on the recording medium 12. Ultraviolet rays are irradiated.

  In FIG. 6, a mounting portion 38 for the ink cartridge 36 is provided on the left front surface of the apparatus main body 20. The ink cartridge 36 is a replaceable ink supply source (ink tank) that stores ultraviolet curable ink. The ink cartridge 36 is provided corresponding to each color ink used in the inkjet recording apparatus 10 of this example. Each color-specific ink cartridge 36 is connected to the inkjet head 24 by an ink supply path (not shown) formed independently. When the remaining amount of ink for each color is low, the ink cartridge 36 is replaced.

  Although not shown, a maintenance unit for the inkjet head 24 is provided on the right side of the apparatus main body 20 toward the front. The maintenance unit is provided with a cap for keeping the ink-jet head 24 moisturized during non-printing and a wiping member (blade, web, etc.) for cleaning the nozzle surface (ink ejection surface) of the ink-jet head 24. The cap for capping the nozzle surface of the inkjet head 24 is provided with an ink receiver for receiving ink droplets ejected from the nozzle for maintenance.

<Description of recording medium conveyance path>
FIG. 7 is an explanatory diagram schematically showing a recording medium conveyance path in the inkjet recording apparatus 10. As shown in FIG. 7, the platen 26 is formed in an inverted bowl shape, and the upper surface thereof serves as a support surface of the recording medium 12 (referred to as “medium support surface”). A pair of nip rollers 40 that are recording medium conveying means for intermittently conveying the recording medium 12 are disposed on the upstream side in the recording medium conveying direction (X direction) in the vicinity of the platen 26. The nip roller 40 moves the recording medium 12 on the platen 26 in the recording medium conveyance direction (X direction).

  The recording medium 12 sent out from a supply-side roll (referred to as a “feed-out supply roll”) 42 that constitutes a roll-to-roll type medium conveying means is fed to the entrance of the printing unit (upstream of the platen 26 in the recording medium conveying direction). Are intermittently conveyed in the X direction by a pair of nip rollers 40 provided on the side). The recording medium 12 that has reached the printing unit immediately below the ink jet head 24 is printed by the ink jet head 24 and is taken up by the take-up roll 44 after printing. A guide 46 for the recording medium 12 is provided on the downstream side of the printing unit in the recording medium conveyance direction.

  A temperature adjusting unit 50 for adjusting the temperature of the recording medium 12 during printing is provided on the back surface (the surface opposite to the surface supporting the recording medium 12) of the platen 26 at a position facing the inkjet head 24 in the printing unit. Is provided. When the recording medium 12 at the time of printing is adjusted to a predetermined temperature, the physical properties such as the viscosity of the ink droplets that have landed on the recording medium 12 and the surface tension become the desired values, and the desired dot diameter is set. Can be obtained. In addition, as needed, the pre temperature control part 52 may be provided in the upstream of the temperature control part 50, and the after temperature control part 54 may be provided in the downstream of the temperature control part 50.

<Description of inkjet head>
FIG. 8 is a plan perspective view showing an example of an arrangement form of the ink jet head 24 arranged on the carriage 30, the temporary curing light sources 32A and 32B, and the main curing light sources 34A and 34B.

  The inkjet head 24 has yellow (Y), magenta (M), cyan (C), black (K), light cyan (LC), light magenta (LM), transparent ink (CL), and white (W) colors. For each ink, nozzle rows 61Y, 61M, 61C, 61K, 61LC, 61LM, 61CL, and 61W are provided for ejecting the respective color inks. In FIG. 8, the nozzle rows are indicated by dotted lines, and individual illustrations of the nozzles are omitted. In the following description, the nozzle rows 61Y, 61M, 61C, 61K, 61LC, 61LM, 61CL, and 61W may be collectively referred to by the reference numeral 61 to represent the nozzle rows.

  The ink color type (number of colors) and the color combination are not limited to the present embodiment. For example, a form in which the LC and LM nozzle arrays are omitted, a form in which the CL and W nozzle arrays are omitted, and a form in which a nozzle array for ejecting special color ink is added are possible. Further, the arrangement order of the nozzle rows for each color is not particularly limited.

  By forming a head module for each color nozzle row 61 and arranging them, it is possible to form an inkjet head 24 capable of color drawing. For example, a head module 24Y having a nozzle row 61Y that discharges yellow ink, a head module 24M having a nozzle row 61M that discharges magenta ink, a head module 24C having a nozzle row 61C that discharges cyan ink, and black ink A head module 24K having a nozzle row 61K for discharging, and head modules 24LC, 24LM, 24CL, 24W having nozzle rows 61LC, 61LM, 61CL, 61W for discharging ink of each color of LC, LM, CL, W, respectively. A mode is also possible in which the carriages 30 are arranged at equal intervals so as to be aligned along the reciprocating direction (main scanning direction) of the carriage 30. The color-specific head modules 24Y, 24M, 24C, 24K, 24LC, and 24LM may be interpreted as “inkjet heads”, respectively. Alternatively, a configuration in which an ink flow path is separately formed for each color within one inkjet head 24 and a nozzle row that ejects a plurality of colors of ink with one head is also possible.

  In each nozzle row 61, a plurality of nozzles are arranged in a row (linearly) along the recording medium conveyance direction (sub-scanning direction) at regular intervals. In the inkjet head 24 of this example, the arrangement pitch (nozzle pitch) of the nozzles constituting each nozzle row 61 is 254 μm (100 dpi), the number of nozzles constituting one nozzle row 61 is 256 nozzles, and the total length of the nozzle row 61 Lw (corresponding to “nozzle row length”, sometimes referred to as “nozzle row width”) is approximately 65 mm (254 μm × 255 = 64.8 mm). Further, the discharge frequency is 15 kHz, and three types of discharge droplet amounts of 10 pl, 20 pl, and 30 pl can be distinguished by changing the drive waveform.

  Note that the nozzle row spacing in the Y direction is not necessarily constant.

  As an ink ejection method of the inkjet head 24, a method (piezo jet method) in which ink droplets are ejected by deformation of a piezoelectric element (piezo actuator) is employed. In addition to a configuration using an electrostatic actuator (electrostatic actuator method) as a discharge energy generating element, a heating element (heating element) such as a heater is used to heat ink to generate bubbles and to eject ink droplets with that pressure. It is also possible to adopt a form (thermal jet system). However, since the ultraviolet curable ink generally has a higher viscosity than the solvent ink, when using the ultraviolet curable ink, it is preferable to adopt a piezo jet method having a relatively large ejection force.

<About the arrangement of the UV irradiation device>
As shown in FIG. 8, provisional curing light sources 32 </ b> A and 32 </ b> B are arranged on the left and right sides of the scanning direction (Y direction) of the inkjet head 24. Further, main curing light sources 34 </ b> A and 34 </ b> B are arranged on the downstream side of the inkjet head 24 in the recording medium conveyance direction (X direction).

  The ink droplets ejected from the nozzles of the ink jet head 24 and landed on the recording medium 12 are immediately irradiated with ultraviolet rays for temporary curing by the temporary curing light source 32A (or 32B) passing thereover. Further, the ink droplets on the recording medium 12 that have passed through the printing area of the inkjet head 24 as the recording medium 12 is intermittently conveyed are irradiated with ultraviolet rays for main curing by the main curing light sources 34A and 34B.

  As shown in FIG. 8, each of the temporary curing light sources 32A and 32B has a structure in which a plurality of UV-LED elements 33 are arranged. The two temporary curing light sources 32A and 32B have a common configuration. In this example, as the temporary curing light sources 32A and 32B, the LED element array in which six UV-LED elements 33 are arranged in a line along the X direction is illustrated, but the number of LED elements and the array form thereof are shown in this example. It is not limited. For example, a configuration in which a plurality of LED elements are arranged in a matrix in the X / Y direction is also possible.

  The six UV-LED elements 33 are arranged so that UV irradiation can be performed at once on a region having the same width as the nozzle row width Lw of the inkjet head 24.

  The main curing light sources 34A and 34B each have a structure in which a plurality of UV-LED elements 35 are arranged. The two main curing light sources 34A and 34B have a common configuration. In this example, as the main curing light sources 34A and 34B, an LED element array (6 × 2) in which six UV-LED elements 35 in the Y direction and two in the X direction are arranged in a matrix is illustrated.

  The number of LED elements of the main curing light source and the arrangement form thereof are not limited to the example of FIG. For example, a configuration in which a plurality of LED elements are arranged in a line along the X direction is also possible.

<About drawing mode>
The inkjet recording apparatus 10 configured as described above is applied with multi-pass drawing control, and the print resolution can be changed by changing the number of print passes. For example, three types of drawing modes, a high production mode, a standard mode, and a high image quality mode, are prepared, and the printing resolution is different in each mode. The drawing mode can be selected according to the printing purpose and application.

  In the high production mode, printing is executed with a resolution of 600 dpi (main scanning direction) × 400 dpi (sub-scanning direction). In the high production mode, a resolution of 600 dpi is realized by two passes (two scans) in the main scanning direction. First, dots are formed with a resolution of 300 dpi in the first scan (the forward path of the carriage 30). In the second scan (return pass), dots are formed such that the middle of the dots formed in the first scan (forward pass) is interpolated at 300 dpi, and a resolution of 600 dpi is obtained in the main scan direction.

  On the other hand, in the sub-scanning direction, the nozzle pitch is 100 dpi, and dots are formed at a resolution of 100 dpi in the sub-scanning direction by one main scanning (one pass). Therefore, a resolution of 400 dpi is realized by performing interpolation printing by four-pass printing (four scans).

  In this specification, the product of the number of passes in the main scanning direction and the number of passes in the sub-scanning direction is referred to as the number of passes in the drawing mode. Therefore, the number of passes in the high production mode is main scanning 2-pass printing × sub-scanning 4-pass printing = 8 passes.

  In the standard mode, printing is performed with a resolution of 600 dpi × 800 dpi. This resolution can be obtained by 2-pass printing in the main scanning direction and 8-pass printing in the sub-scanning direction. That is, the number of passes in the standard mode is main scanning 2-pass printing × sub-scanning 8-pass printing = 16 passes.

  In the high image quality mode, printing is executed at a resolution of 1200 × 1200 dpi, and this resolution is obtained by 4 passes in the main scanning direction and 12 passes in the sub-scanning direction. That is, the number of passes in the high image quality mode is main scanning 4 pass printing × sub scanning 12 pass printing = 48 passes.

  The main scanning speed of the carriage 30 is 1270 mm / sec in each mode.

  In this way, even if the number of passes differs depending on the drawing mode, temporary curing and main curing can be performed with an appropriate amount of light.

<Description of ink supply system>
FIG. 9 is a block diagram showing the configuration of the ink supply system of the inkjet recording apparatus 10. As shown in the figure, the ink stored in the ink cartridge 36 is sucked by the supply pump 70 and sent to the inkjet head 24 via the sub tank 72. The sub tank 72 is provided with a pressure adjusting unit 74 for adjusting the pressure of the ink inside.

  The pressure adjusting unit 74 includes a pressure increasing / decreasing pump 77 communicating with the sub tank 72 via the valve 76, and a pressure gauge 78 provided between the valve 76 and the pressure increasing / decreasing pump 77.

  During normal printing, the pressure increasing / decreasing pump 77 operates in the direction of sucking ink in the sub tank 72, and the internal pressure of the sub tank 72 and the internal pressure of the inkjet head 24 are maintained at negative pressure. On the other hand, at the time of maintenance of the ink jet head 24, the pressure increasing / decreasing pump 77 operates to pressurize the ink in the sub tank 72, and the inside of the sub tank 72 and the inside of the ink jet head 24 are forcibly pressurized. The ink inside is discharged through the nozzle. The ink forcibly discharged from the inkjet head 24 is accommodated in the ink receiver of the cap (not shown) described above.

<Description of Control System of Inkjet Recording Apparatus>
FIG. 10 is a block diagram showing the configuration of the inkjet recording apparatus 10. As shown in the figure, the ink jet recording apparatus 10 is provided with a control device 102 as control means. As the control device 102, for example, a computer having a central processing unit (CPU) can be used. The control device 102 functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as a calculation device that performs various calculations. The control device 102 includes a recording medium conveyance control unit 104, a carriage drive control unit 106, a light source control unit 108, an image processing unit 110, and an ejection control unit 112. Each of these units is realized by a hardware circuit or software, or a combination thereof.

  The recording medium conveyance control unit 104 controls the conveyance driving unit 114 for conveying the recording medium 12 (see FIG. 1). The conveyance drive unit 114 includes a drive motor that drives the nip roller 40 shown in FIG. 2 and a drive circuit thereof. The recording medium 12 conveyed on the platen 26 (see FIG. 1) is intermittently fed in the sub-scanning direction in units of swath widths in accordance with the reciprocating scanning (movement of the printing pass) in the main scanning direction by the inkjet head 24.

  A carriage drive control unit 106 shown in FIG. 14 controls a main scanning drive unit 116 for moving the carriage 30 (see FIG. 1) in the main scanning direction. The main scanning drive unit 116 includes a drive motor connected to a moving mechanism of the carriage 30 and a control circuit thereof.

  The light source control unit 108 adjusts the amount of light emitted from the UV-LED elements 33 of the temporary curing light sources 32A and 32B via the LED drive circuit 118, and the UV-LEDs of the main curing light sources 34A and 34B via the LED drive circuit 119. It is a control means for adjusting the light emission amount of the element 35.

  The LED drive circuit 118 adjusts the light emission amount of the UV-LED element 33 by outputting a voltage having a voltage value corresponding to a command from the light source control unit 108. The LED drive circuit 119 adjusts the light emission amount of the UV-LED element 35 by outputting a voltage having a voltage value corresponding to a command from the light source control unit 108. The light emission amount of the LED may be adjusted by changing the duty or frequency of the drive waveform instead of changing the voltage.

  The adjustment of the ink exposure amount in the present embodiment is not limited to the control of the light emission amount according to the command from the light source control unit 108. For example, the exposure amount may be adjusted by replacing the temporary curing light sources 32A and 32B and the main curing light sources 34A and 34B for each drawing mode so that exposure according to the number of passes can be performed.

  The control device 102 is connected to an input device 120 such as an operation panel and a display device 122.

  The input device 120 is means for inputting a manual external operation signal to the control device 102. For example, various forms such as a keyboard, a mouse, a touch panel, and operation buttons can be adopted. Various forms such as a liquid crystal display, an organic EL display, and a CRT can be adopted as the display device 122. By operating the input device 120, the operator can select a drawing mode, input printing conditions, and input / edit attached information. Various information such as input contents and search results are stored on the display device 122. It can be confirmed through the display.

  Further, the ink jet recording apparatus 10 is provided with an information storage unit 124 for storing various types of information and an image input interface 126 for taking in image data for printing. As the image input interface, a serial interface or a parallel interface may be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data input via the image input interface 126 is converted into print data (dot data) by the image processing unit 110. The dot data is generally generated by performing color conversion processing and halftone processing on multi-tone image data. The color conversion process is a process of converting image data expressed in sRGB or the like (for example, 8-bit image data for each RGB color) into color data for each ink color used in the inkjet recording apparatus 10.

  The halftone process is a process for converting the color data of each color generated by the color conversion process into dot data of each color by a process such as an error diffusion method or a threshold matrix. Various known means such as an error diffusion method, a dither method, a threshold matrix method, and a density pattern method can be applied as the halftone processing means. The halftone process generally converts gradation image data having an M value (M ≧ 3) into gradation image data having an N value (N <M). In the simplest example, it is converted into binary (dot on / off) dot image data, but in halftone processing, it corresponds to the dot size type (for example, three types such as large dot, medium dot, small dot). It is also possible to perform multi-level quantization.

  The binary or multi-valued image data (dot data) obtained in this way controls the drive (on) / non-drive (off) of each nozzle, and in the case of multiple values, controls the droplet amount (dot size). Used as ink ejection data (droplet ejection control data).

  The ejection control unit 112 includes the waveform generation unit 142 and the signal selection unit 146 shown in FIG. 1, and based on the dot data generated by the image processing unit 110, the ejection control signal is sent to the head drive circuit 128. Is generated.

  A common drive voltage signal is applied to each ejection energy generation element of the inkjet head 25 via the head drive circuit 128, and the switch element is connected to the individual electrode of each energy generation element according to the ejection timing of each nozzle. By switching on / off (not shown), ink is ejected from the corresponding nozzle.

  The information storage unit 124 stores programs executed by the CPU of the control device 102, various data necessary for control, and the like. The information storage unit 124 stores resolution setting information according to the drawing mode, the number of passes (the number of scan repetitions), light emission amount information of the temporary curing light sources 32A and 32B, and the main curing light sources 34A and 34B.

  The encoder 130 is attached to the drive motor of the main scanning drive unit 116 and the drive motor of the transport drive unit 114, and outputs a pulse signal corresponding to the rotation amount and rotation speed of the drive motor. Is sent to the controller 102. Based on the pulse signal output from the encoder 130, the position of the carriage 30 and the position of the recording medium 12 (see FIG. 1) are grasped.

  The sensor 132 is attached to the carriage 30, and the width of the recording medium 12 is grasped based on the sensor signal obtained from the sensor 132.

  In the above embodiment, an example in which the drawing head unit (inkjet head 24) has one nozzle row for each color has been described, but the nozzle arrangement is not limited to this example. For example, for each color, a two-row zigzag arrangement, or a multi-row matrix arrangement or other two-dimensional arrangement may be used.

  In the above-described embodiment, the wide format ink jet recording apparatus is exemplified, but the scope of application of the present invention is not limited to this. Application to inkjet recording apparatuses other than the wide format is also possible. In addition, the present invention is not limited to graphic printing applications, electronic circuit board wiring drawing apparatuses, various device manufacturing apparatuses, resist printing apparatuses that use a resin liquid as a functional liquid for ejection (corresponding to “ink”), The present invention can be applied to various image forming apparatuses that can form various image patterns such as a fine structure forming apparatus.

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Recording medium, 24 ... Inkjet head, 100 ... Inkjet ejection device, 128 ... Head drive circuit, 140 ... Drive device, 142 ... Waveform generator, 150 ... Pressure chamber, 152 ... Nozzle, 160 ... Piezoelectric actuator, 162 ... upper electrode, 164 ... lower electrode, 166 ... piezoelectric pair, 220 ... drive signal, 222 ... discharge pulse, 225 ... pressure suppression pulse

Claims (8)

In a waveform generation device that generates a drive waveform to be supplied to an actuator of an inkjet head, comprising: a nozzle that discharges a droplet; a liquid chamber that communicates with the nozzle; and an actuator that pressurizes the liquid in the liquid chamber.
Discharge waveform elements for discharging droplets from the nozzles, n (n ≧ 3) discharge waveform elements that excite resonance of the inkjet head are arranged at equal intervals, and the mth (2 ≦ m) from the front A waveform generation apparatus that generates a drive waveform having a non-discharge waveform element that does not discharge a droplet between the discharge waveform element of <n) and the (m + 1) th discharge waveform element.   The waveform generation apparatus according to claim 1, wherein the n ejection waveform elements are waveform elements having the same time width.   The waveform generating apparatus according to claim 1, wherein an interval between the n ejection waveform elements is in a range of 90 to 110% of a resonance period of the inkjet head.   The waveform generating apparatus according to claim 1, wherein the ejection waveform element is a rectangular wave or a trapezoidal wave.   The waveform generation device according to claim 1, wherein the non-ejection waveform element is a rectangular wave or a trapezoidal wave.   The waveform generation apparatus according to claim 1, wherein a width of the non-ejection waveform element is equal to or less than a width of the ejection waveform element.   The amplitude of the non-ejection waveform element is equal to or less than an average of the amplitude of the mth ejection waveform element from the front and the amplitude of the m + 1th ejection waveform element from the front. The waveform generation device according to any one of the above. A waveform generator according to any one of claims 1 to 7,
An inkjet head comprising: a nozzle that discharges droplets; a liquid chamber that communicates with the nozzle; and an actuator that pressurizes the liquid in the liquid chamber;
Driving means for supplying the generated driving waveform to the actuator to shoot droplets from the nozzles n times;
Moving means for relatively moving the recording object and the inkjet head;
An ink jet recording apparatus comprising:

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