JP2015058582A - Droplet discharge device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a droplet discharge device capable of preventing occurence of satellites effectively.SOLUTION: A drive signal W to be applied to an actuator which provided in a pressure chamber for discharging a droplet from a nozzle is composed of a discharge pulse DP, a first draw-in pulse PP1 and a second draw-in pulse PP2. The first draw-in pulse PP1 is set so as to be applied within the range of (1/2)×Tc to (5/8)×Tc after application of the discharge pulse DP, and the second draw-in pulse PP2 is set so as to be applied within the range of (3/4)×Tc to Tc after application of the discharge pulse DP.

Description

  The present invention relates to a droplet discharge device, and more particularly to a droplet discharge device that discharges droplets from a nozzle by expanding / contracting a pressure chamber communicated with the nozzle with an actuator.

  In a droplet discharge device that discharges droplets from a nozzle by expanding / contracting the pressure chamber connected to the nozzle with an actuator, a very small droplet called a satellite (also called “mist”) is discharged during discharge. It may occur after the applied droplet. Satellites have the problem that they adhere to the droplet ejection target and degrade the image quality, or adhere to the nozzle surface and cause ejection defects.

  Such satellites are generated when the rear end portion of a droplet discharged from a nozzle extends like a tail and separates into any number. Patent Document 1 proposes a method for suppressing the occurrence of satellites by applying a drive signal having a predetermined waveform to an actuator to suppress the phenomenon that the trailing edge of the droplet extends like a tail. Specifically, a discharge drive pulse to be applied to the actuator includes a first pressure chamber expansion element that expands the pressure chamber and draws the meniscus toward the pressure chamber, and a pressure chamber expanded by the first pressure chamber expansion element. A pressure chamber contraction element that contracts and pushes out the meniscus to the discharge side, a second pressure chamber expansion element that expands the pressure chamber contracted by the pressure chamber contraction element and draws the meniscus to the pressure chamber side, and A first retracting element that expands the pressure chamber contracted by the pressure chamber contracting element to the first intermediate expansion volume and retracts the meniscus toward the pressure chamber; and a first intermediate expansion of the pressure chamber. By comprising an intermediate maintenance element that maintains the volume for a certain period of time and a second retraction element that expands from the first intermediate expansion volume to the second intermediate expansion volume to further draw the meniscus The rear end of the discharged allowed droplets is suppressed phenomenon extending like a tail.

JP 2010-179585 JP

  However, the method of Patent Document 1 has not sufficiently solved the problem from the viewpoint of preventing satellites. In other words, Patent Document 1 has not only the prevention of satellites but also the problem of miniaturization of droplets, and since the waveform of the ejection drive pulse is set to simultaneously achieve the problem, the generation of satellites is sufficiently suppressed. It was not done.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a droplet discharge device that can effectively prevent the generation of satellites.

  Means for solving the problems are as follows.

  A first aspect includes a droplet discharge head having a nozzle, a pressure chamber communicating with the nozzle, and an actuator that expands / contracts the pressure chamber, a drive signal generation unit that generates a drive signal to be applied to the actuator, The drive signal generated by the drive signal generation unit is applied after applying the at least one discharge pulse for discharging the droplet from the nozzle and the final discharge pulse, and draws the meniscus to the pressure chamber side. And a second pulling pulse that is applied after applying the first pulling pulse and pulls the meniscus to the pressure chamber side, and the Helmholtz period determined from the structure of the droplet discharge head is Tc In this case, the ejection pulse width is set to (1/2) × Tc or less, and the application start point of the first pulling pulse is generated by applying the ejection pulse. It is set within a range of (1/8) × Tc from the point when the niscus vibration becomes zero crossing, and the application start point of the second pulling pulse is maximized on the ejection side when the meniscus vibration generated by applying the ejection pulse is applied. The droplet discharge device is set within a range of (1/4) × Tc from the time point.

  According to this aspect, after applying the final ejection pulse, the first pulling pulse and the second pulling pulse are applied. The first pulling pulse is set within a range of (1/8) × Tc from the point in time when the meniscus vibration generated by applying the discharge pulse becomes zero cross, and the second pulling pulse applies the discharge pulse. This is set within a range of (1/4) × Tc from the point in time when the meniscus vibration generated by this is maximized on the discharge side. That is, the application timing of the first pulling pulse and the application timing of the second pulling pulse are set based on the meniscus vibration when the ejection pulse is applied. The first pulling pulse is set so as to be applied after the point at which the meniscus position switches from the pressure chamber side to the discharge side (zero cross point), and the second pulling pulse has maximum meniscus vibration on the discharge side. It is set to be applied after the point. As a result, the droplets can be efficiently separated using the vibration of the meniscus, and the generation of satellites can be effectively suppressed.

  Note that the final ejection pulse means the ejection pulse that is applied last, for example, when the dot size is changed by changing the number of ejection pulses.

  The second mode is a mode in which the final ejection pulse width is set to be 5% to 15% narrower than (1/2) × Tc in the droplet ejection device of the first mode.

  According to this aspect, the width of the final ejection pulse is set to be 5% to 15% narrower than (1/2) × Tc. The satellite suppression effect increases as the timing at which the first pulling pulse is applied approaches the zero cross point. The timing of applying the first pulling pulse can be closer to the zero cross point as the width of the final ejection pulse is narrowed, that is, as the end point of the final ejection pulse is advanced. On the other hand, when the width of the ejection pulse is narrowed, the speed of the ejected droplet is reduced by applying the ejection pulse. According to this aspect, it is possible to apply the first pulling pulse as close to the zero cross point as possible while maintaining a sufficient droplet velocity, and it is possible to more effectively suppress the generation of satellites.

  The third aspect is an aspect in which, in the droplet discharge device of the second aspect, the application start point of the first pulling pulse is set to a point where the meniscus vibration generated by applying the discharge pulse becomes zero cross. is there.

  As described above, as the first pulling pulse is applied near the zero cross point, the satellite suppression effect is enhanced. According to this aspect, since the first pulling pulse is applied at the zero cross point of the meniscus vibration, the generation of satellites can be more effectively suppressed.

  In the fourth aspect, in the liquid droplet ejection apparatus of the third aspect, the application start point of the second pulling pulse is set to a point where the meniscus vibration generated by applying the ejection pulse is maximized on the ejection side. This is a mode.

  According to this aspect, the second pulling pulse is applied when the meniscus position becomes maximum on the ejection side. By applying the second pulling pulse when the meniscus position becomes maximum on the discharge side, the meniscus can be pulled most effectively and the generation of satellites can be more effectively suppressed.

  A fifth aspect includes a droplet discharge head having a nozzle, a pressure chamber communicating with the nozzle, and an actuator that expands / contracts the pressure chamber, a drive signal generation unit that generates a drive signal to be applied to the actuator, The drive signal generated by the drive signal generation unit is applied after applying the at least one discharge pulse for discharging the droplet from the nozzle and the final discharge pulse, and draws the meniscus to the pressure chamber side. And a second pulling pulse that is applied after applying the first pulling pulse and pulls the meniscus to the pressure chamber side, and the Helmholtz period determined from the structure of the droplet discharge head is Tc In this case, the width of the ejection pulse is set to (1/2) × Tc or less, and the application start point of the first pulling pulse is (1/2) after the application start of the final ejection pulse. It is set within the range of not less than × Tc and not more than (5/8) × Tc, and the application start point of the second pulling pulse is not less than (3/4) × Tc and less than Tc after the start of application of the final ejection pulse It is a droplet discharge device set within the range.

  According to this aspect, after applying the final ejection pulse, the first pulling pulse and the second pulling pulse are applied. The first pulling pulse is applied within the range of (1/2) × Tc to (5/8) × Tc after the start of the application of the final ejection pulse, and the second pulling pulse is the final ejection pulse. After the start of application, it is applied within the range of (3/4) × Tc to Tc. That is, the application timing of the first pulling pulse and the application timing of the second pulling pulse are set based on the meniscus vibration estimated to occur when the final ejection pulse is applied. The first pulling pulse is applied after the point at which the meniscus position is estimated to switch from the pressure chamber side to the discharge side ((1/2) × Tc point after starting the application of the final discharge pulse). And the second pulling pulse is applied after the point where the meniscus vibration is estimated to be maximum on the discharge side (the point of (3/4) × Tc after starting the application of the final discharge pulse). Set to As a result, the droplets can be efficiently separated using the vibration of the meniscus, and the generation of satellites can be effectively suppressed.

  The sixth aspect is an aspect in which, in the droplet discharge device of the fifth aspect, the width of the final discharge pulse is set to be narrower by 5% to 15% than (1/2) × Tc.

  According to this aspect, the width of the final ejection pulse is set to be 5% to 15% narrower than (1/2) × Tc. Accordingly, the first pulling pulse can be applied as close to the zero cross point as possible while maintaining a sufficient droplet velocity, and the generation of satellites can be more effectively suppressed.

  According to a seventh aspect, in the liquid droplet ejection apparatus according to the sixth aspect, the application start point of the first pulling pulse is set to a point of (1/2) × Tc after the application of the final ejection pulse is started. It is an aspect.

  According to this aspect, since the first pulling pulse is applied at the point where the meniscus vibration is estimated to be zero-crossed, the generation of satellites can be more effectively suppressed.

  According to an eighth aspect, in the liquid droplet ejection apparatus according to the seventh aspect, the application start point of the second pulling pulse is set to a point of (3/4) × Tc after the application of the final ejection pulse is started. It is an aspect.

  According to this aspect, the second pulling pulse is applied when the meniscus position is estimated to be maximum on the ejection side. Thereby, the meniscus can be pulled most effectively and the generation of satellites can be more effectively suppressed.

  A ninth aspect includes a droplet discharge head including a nozzle, a pressure chamber communicating with the nozzle, and an actuator that expands / contracts the pressure chamber, a drive signal generation unit that generates a drive signal applied to the actuator, The drive signal generated by the drive signal generator includes at least one ejection pulse for ejecting droplets from the nozzle, a first pressure chamber expansion element for expanding the pressure chamber to the first volume, A maintenance element for maintaining the volume of the pressure chamber expanded to the first volume by the pressure chamber expansion element; a second pressure chamber expansion element for expanding the volume of the pressure chamber from the first volume to the second volume; A pressure chamber contraction element that contracts the pressure chamber, and a pulling pulse that is applied after the final ejection pulse is applied to draw the meniscus stepwise toward the pressure chamber, and is obtained from the structure of the droplet ejection head. When the Helmholtz period is Tc, the discharge pulse width is set to ½ Tc or less, and the starting point of the first pressure chamber expansion element is the time when the meniscus vibration generated by applying the discharge pulse becomes zero cross From the time point when the meniscus vibration generated by applying the discharge pulse becomes maximum on the discharge side (1/8) × Tc. / 4) It is a droplet discharge device set within a range of within * Tc.

  According to this aspect, after applying the final ejection pulse, the pulling pulse is applied. The pulling pulse includes a first pressure chamber expansion element that expands the pressure chamber to a first volume, and a maintenance element that maintains the volume of the pressure chamber expanded to the first volume by the first pressure chamber expansion element; A second pressure chamber expansion element that expands the volume of the pressure chamber from the first volume to the second volume; and a pressure chamber contraction element that contracts the pressure chamber, wherein the first pressure chamber expansion element includes a discharge pulse. Is set within a range of (1/8) × Tc from the point in time when the meniscus vibration generated by applying a zero cross. Further, the second pressure chamber expansion element is set within a range of (1/4) × Tc from the point in time at which the meniscus vibration generated by applying the discharge pulse becomes maximum on the discharge side. That is, the start point of the first pressure chamber expansion element and the start point of the second pressure chamber expansion element are set based on the meniscus vibration when the ejection pulse is applied. The first pressure chamber expansion element is set to start after a point (zero cross point) at which the meniscus position switches from the pressure chamber side to the discharge side, and the second pressure chamber expansion element has a meniscus vibration on the discharge side. It is set to start after the point where the maximum is reached. As a result, the droplets can be efficiently separated using the vibration of the meniscus, and the generation of satellites can be effectively suppressed.

  The tenth aspect is an aspect in which, in the liquid droplet ejection apparatus of the ninth aspect, the width of the ejection pulse is set to be narrower by 5% to 15% than (1/2) × Tc.

  According to this aspect, the width of the final ejection pulse is set to be 5% to 15% narrower than (1/2) × Tc. Accordingly, the first pressure chamber expansion element can be set as close to the zero cross point as possible while maintaining a sufficient droplet velocity, and the generation of satellites can be more effectively suppressed.

  The eleventh aspect is an aspect in which, in the droplet discharge device of the tenth aspect, the start point of the first pressure chamber expansion element is set to a point where the meniscus vibration generated by applying the discharge pulse becomes zero cross. It is.

  According to this aspect, since the starting point of the first pressure chamber expansion element is set to a point where the meniscus vibration becomes zero cross, generation of satellites can be more effectively suppressed.

  In a twelfth aspect, in the droplet discharge device according to the eleventh aspect, the starting point of the second pressure chamber expansion element is set to a point at which meniscus vibration generated by applying a discharge pulse is maximized on the discharge side. It is an embodiment.

  According to this aspect, since the starting point of the second pressure chamber expansion element is set to a point where the meniscus position is maximized on the discharge side, the generation of satellites can be more effectively suppressed.

  A thirteenth aspect includes a droplet discharge head having a nozzle, a pressure chamber communicating with the nozzle, and an actuator that expands / contracts the pressure chamber, a drive signal generation unit that generates a drive signal applied to the actuator, The drive signal generated by the drive signal generator includes at least one ejection pulse for ejecting droplets from the nozzle, a first pressure chamber expansion element for expanding the pressure chamber to the first volume, A maintenance element for maintaining the volume of the pressure chamber expanded to the first volume by the pressure chamber expansion element; a second pressure chamber expansion element for expanding the volume of the pressure chamber from the first volume to the second volume; A pressure chamber contraction element that contracts the pressure chamber, and a pulling pulse that is applied after the final ejection pulse is applied, and draws the meniscus stepwise toward the pressure chamber, from the structure of the droplet ejection head When the Helmholtz period is Tc, the discharge pulse width is set to 1/2 Tc or less, and the starting point of the first pressure chamber expansion element is (1/2) × It is set within the range of Tc or more and (5/8) × Tc or less, and the start point of the second pressure chamber expansion element is (3/4) × Tc or more and less than Tc after the start of application of the final ejection pulse. It is a droplet discharge device set within the range.

  According to this aspect, after applying the final ejection pulse, the pulling pulse is applied. The pulling pulse includes a first pressure chamber expansion element that expands the pressure chamber to a first volume, and a maintenance element that maintains the volume of the pressure chamber expanded to the first volume by the first pressure chamber expansion element; A second pressure chamber expansion element that expands the pressure chamber volume from the first volume to the second volume; and a pressure chamber contraction element that contracts the pressure chamber, the starting point of the first pressure chamber expansion element is This is set after the zero cross point of the meniscus vibration estimated to be generated by applying the ejection pulse ((1/2) × Tc point after the start of the final ejection pulse application). The starting point of the second pressure chamber expansion element is the maximum point on the discharge side of the meniscus vibration that is estimated to be generated by applying the discharge pulse ((3/4) × after the start of the final discharge pulse application). It is set after the point Tc). That is, the start point of the first pressure chamber expansion element and the start point of the second pressure chamber expansion element are set based on the meniscus vibration estimated to occur when the ejection pulse is applied. The first pressure chamber expansion element is set to start after the point (zero cross point) where the meniscus position is estimated to switch from the pressure chamber side to the discharge side, and the second pressure chamber expansion element is It is set to start after the estimated point where the vibration becomes maximum on the discharge side. As a result, the droplets can be efficiently separated using the vibration of the meniscus, and the generation of satellites can be effectively suppressed.

  The fourteenth aspect is an aspect in which, in the liquid droplet ejection apparatus of the thirteenth aspect, the width of the ejection pulse is set to be narrower by 5% to 15% than (1/2) × Tc.

  According to this aspect, the width of the final ejection pulse is set to be 5% to 15% narrower than (1/2) × Tc. Accordingly, the first pressure chamber expansion element can be set as close to the zero cross point as possible while maintaining a sufficient droplet velocity, and the generation of satellites can be more effectively suppressed.

  According to a fifteenth aspect, in the droplet discharge device according to the fourteenth aspect, the start point of the first pressure chamber expansion element is set to a point of (1/2) × Tc after the start of application of the final discharge pulse. This is a mode.

  According to this aspect, since the starting point of the first pressure chamber expansion element is set to a point estimated as the zero cross point of meniscus vibration, the generation of satellites can be more effectively suppressed.

  According to a sixteenth aspect, in the droplet discharge device according to the fifteenth aspect, the start point of the second pressure chamber expansion element is set to a point of (3/4) × Tc after the start of application of the final discharge pulse. This is a mode.

  According to this aspect, since the starting point of the second pressure chamber expansion element is set to a point where the meniscus position is estimated to be maximum on the discharge side, the generation of satellites can be more effectively suppressed. .

  According to the present invention, generation of satellites can be effectively prevented.

1 is a system configuration diagram showing an embodiment of a droplet discharge apparatus according to the present invention. Top view of the nozzle surface of the droplet discharge head Longitudinal sectional view showing the schematic structure inside the droplet discharge head Waveform diagram of the driving signal for one droplet ejection period generated by the driving device Graph showing time displacement of meniscus position when ejection pulse DP is applied Table showing experimental results Table showing experimental results The wave form diagram which shows the modification of the drive signal for 1 droplet ejection period which a drive device produces | generates Waveform diagram showing an example of the drive signal when changing the dot diameter Overall configuration diagram of inkjet recording apparatus Schematic configuration diagram of inkjet head Partial enlarged view of inkjet head Plan view showing nozzle arrangement of head module Block diagram showing the system configuration of the control system of the inkjet recording apparatus 310

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

<Configuration of droplet discharge device>
FIG. 1 is a system configuration diagram showing an embodiment of a droplet discharge apparatus according to the present invention.

  The droplet discharge device 1 according to the present embodiment is configured as an image recording device that records an image on a medium, and includes a droplet discharge head 10 that discharges droplets onto a medium, an image processing device 100, and a drive device 200. It is prepared for.

  The droplet discharge head 10 is of a piezoelectric method (a method of discharging droplets using a reverse piezoelectric effect (displacement occurs when a voltage is applied) of a piezoelectric material typified by PZT (lead zirconate titanate)). It is composed of a droplet discharge head. Although details will be described later, the droplet discharge head 10 includes a plurality of nozzles, and the actuator 20 expands / contracts the volume of the pressure chamber communicated with each nozzle, thereby discharging droplets from each nozzle.

  The image processing apparatus 100 acquires image data (for example, RGB format image data) of an image to be recorded on a medium, and converts it into a data format (dot arrangement data) that can be recorded by the droplet discharge head 10. Specifically, the acquired image data is subjected to necessary signal processing such as color conversion processing and halftone processing to generate dot arrangement data.

  The drive device 200 functions as a drive waveform generation unit, and generates a drive signal for driving each actuator of the droplet discharge head 10 based on the dot arrangement data generated by the image processing device 100.

<Configuration of droplet discharge head>
The droplet discharge head 10 includes a nozzle surface 12, and a number of nozzles 14 are arranged on the nozzle surface 12.

  FIG. 2 is a plan view of the nozzle surface of the droplet discharge head.

  As shown in FIG. 2, the nozzle surface 12 has a rectangular shape, and a plurality of nozzles 14 are arranged in a line at a constant pitch along the longitudinal direction. Inside the droplet discharge head 10, a pressure chamber 16 is provided corresponding to each nozzle 14. Each nozzle 14 is individually communicated with a corresponding pressure chamber 16.

  FIG. 3 is a longitudinal sectional view showing a schematic structure inside the droplet discharge head.

  As shown in FIG. 3, the pressure chamber 16 is provided inside the head as a space for storing liquid. The ceiling of the pressure chamber 16 is composed of a diaphragm 18 and is formed to be deformable in the vertical direction. The nozzle 14 communicates with the center of the bottom surface of the pressure chamber 16.

  A piezoelectric element as the actuator 20 is disposed on the vibration plate 18. The piezoelectric element as the actuator 20 is driven by applying a driving voltage between an individual electrode (not shown) provided on the actuator 20 and a diaphragm 18 acting as a common electrode, and the diaphragm 18 is moved up and down. Deform. Thereby, the pressure chamber 16 expands / contracts (the volume in the pressure chamber expands / contracts).

  The liquid discharged from the nozzle 14 is circulated and supplied to the droplet discharge head 10. As shown in FIG. 2, the droplet discharge head 10 includes a liquid supply port 22 and a recovery port 24.

  Inside the droplet discharge head 10, a common supply channel 26 and a common recovery channel 28 are provided along the arrangement direction of the pressure chambers 16 (longitudinal direction of the droplet discharge head 10). The common supply channel 26 is in communication with the supply port 22, and the common recovery channel 28 is in communication with the recovery port 24. Each pressure chamber 16 communicates with the common supply flow path 26 via the individual supply flow path 30 and communicates with the common recovery flow path 28 via the individual recovery flow path 32.

  When the liquid is supplied from the supply port 22, the liquid is supplied to each pressure chamber 16 via the common supply channel 26 and the individual supply channel 30. The liquid supplied to each pressure chamber 16 is recovered from the recovery port 24 via the individual recovery channel 32 and the common recovery channel 28. Therefore, when the liquid is continuously supplied from the supply port 22 and the liquid is continuously recovered from the recovery port 24, a liquid flow can be formed in the head, and the liquid is circulated to the droplet discharge head 10. Can be supplied.

  The liquid discharged from the nozzle 14 is circulated and supplied to the droplet discharge head 10 by a liquid supply device (not shown).

<< Driving method of droplet discharge head >>
As described above, the droplet discharge head 10 discharges droplets from each nozzle 14 by applying a drive signal having a predetermined waveform to the actuator 20 provided corresponding to each nozzle 14.

  The drive signal is applied to the actuator 20 according to a fixed droplet ejection period. When the drive signal is applied, the actuator 20 is deformed according to the drive waveform indicated by the drive signal, and ejects a droplet from the corresponding nozzle 14.

  The driving device 200 applies a driving signal to the actuator 20 of the nozzle 14 that discharges droplets based on the dot arrangement data.

  FIG. 4 is a waveform diagram of a driving signal for one droplet ejection period generated by the driving device.

  As shown in FIG. 4, the drive signal W applied to the actuator 20 includes an ejection pulse DP for ejecting droplets from the nozzle, and two pull pulses (first pull pulse PP1 and second pull pulse PP2). And.

  The ejection pulse DP is a pulse for ejecting a predetermined amount of droplets from the nozzle 14. The discharge pulse DP has a trapezoidal shape, a pressure chamber expansion element DP-1 for expanding the pressure chamber 16, a maintenance element DP-2 for maintaining the expanded state for a certain period, and an original state in which the pressure chamber 16 is contracted And the pressure chamber contraction element DP-3 to be returned to. When the ejection pulse DP is applied to the actuator 20, the pressure chamber 16 expands / contracts, and a predetermined amount of liquid droplets are ejected from the nozzle 14.

  The pulse width of this discharge pulse DP (the time from the start point of the pressure chamber expansion element DP-1 to the end point of the pressure chamber contraction element DP-3) is expressed as follows, assuming that the Helmholtz period obtained from the structure of the droplet discharge head 10 is Tc: 1/2) × Tc. Thereby, a droplet can be discharged efficiently.

  The first pulling pulse PP1 is a pulse for pulling the meniscus toward the pressure chamber, and is applied subsequent to the ejection pulse DP. The first pulling pulse PP1 has a trapezoidal shape, and the pressure chamber expansion element PP1-1 for expanding the pressure chamber 16, the maintenance element PP1-2 for maintaining the expanded state for a certain period, and the pressure chamber 16 contracted. The pressure chamber contraction element PP1-3 is returned to the original state. When the first pulling pulse PP1 is applied to the actuator 20, the meniscus is drawn to the pressure chamber side, and there is an action of cutting a portion extending like a tail from the rear end portion of the droplet ejected by the ejection pulse DP. work.

  When the ejection pulse DP is applied to the actuator 20, the droplet is ejected from the nozzle 14 with its rear end portion extending like a tail. By applying the first pulling pulse PP1 and pulling the meniscus toward the pressure chamber, the periphery of the portion extending like the tail is pulled toward the pressure chamber and acts to cut the tail portion.

  In the drive signal W shown in FIG. 4, the first pulling pulse PP1 is set to be applied after (9/16) × Tc has elapsed after the start of application of the ejection pulse DP.

  The second pulling pulse PP2 is a pulse for pulling the meniscus toward the pressure chamber, and is applied subsequent to the first pulling pulse PP1. The second pulling pulse PP2 has a trapezoidal shape, the pressure chamber expansion element PP2-1 for expanding the pressure chamber 16, the maintenance element PP2-2 for maintaining the expanded state for a certain period, and the pressure chamber 16 contracted. It is comprised with the pressure chamber contraction element PP2-3 which returns to an original state. By applying the second pulling pulse PP2 to the actuator 20, the meniscus is again pulled to the pressure chamber side, and the action of cutting the tail portion again occurs.

  In the drive signal W shown in FIG. 4, the second pulling pulse PP2 is set to be applied after (3/4) × Tc has elapsed after the start of application of the ejection pulse DP.

  In this way, by applying two pulling pulses (first pulling pulse PP1 and second pulling pulse PP2) subsequent to the discharge pulse DP, the tail from the trailing edge of the droplet during discharge The extending part can be cut short, and the generation of satellites can be suppressed.

  As described above, the drive signal W of the present embodiment includes the ejection pulse DP and the two pull pulses (first pull pulse PP1 and second pull pulse PP2). The timing of applying two pull pulses (first pull pulse PP1 and second pull pulse PP2) is set as follows. That is, the first pulling pulse PP1 is applied within the range of (1/2) × Tc or more and (5/8) × Tc or less (the range A in FIGS. 4 and 5) after the application of the ejection pulse DP is started. The second pulling pulse PP2 is applied within the range of (3/4) × Tc or more and less than Tc (range B in FIGS. 4 and 5) after the application of the ejection pulse DP is started. Is set to This is based on the following reason.

  FIG. 5 is a graph showing the time displacement of the meniscus position when the ejection pulse DP is applied.

  Considering the behavior of the meniscus when the discharge pulse DP is applied, the first pulling pulse PP1 is applied at the point where the meniscus position switches from the pressure chamber side to the discharge side, that is, at the zero cross point WZ of the meniscus vibration. Most effective. On the other hand, it is most effective to apply the second pulling pulse at a point where the meniscus position is switched from the discharge side to the pressure chamber side, that is, at a point where the meniscus vibration becomes maximum on the discharge side (maximum point) WP. That is, by applying the first pulling pulse PP1 at the zero crossing point WZ of the meniscus vibration, it is possible to prevent the liquid from being discharged more than necessary and extending like a tail, and further, the second pulling pulse is applied to the meniscus vibration. By applying at the maximum point WP on the discharge side, the energy on the pull side can be accelerated and the tail portion can be cut efficiently.

  Thus, the first pulling pulse PP1 is set to be applied at the point WZ where the meniscus vibration generated when the discharge pulse DP is applied is zero crossing, and the meniscus vibration is discharged from the second pulling pulse. By setting so as to be applied at a point WP that is maximal on the side, the tail portion can be cut efficiently.

  Here, since it is considered that the meniscus vibration when the ejection pulse DP is applied is generated at a period of Tc, the zero cross point WZ of the meniscus vibration is approximately (1/2) × Tc after the application of the ejection pulse DP is started. It is assumed that it occurs at a location. Further, the point WP where the meniscus vibration becomes maximum on the discharge side is assumed to occur at a position of approximately (3/4) × Tc after the start of application of the discharge pulse DP.

  Therefore, by setting the first pulling pulse PP1 to be applied at the position of (1/2) × Tc, the same effect as that obtained when applied at the zero cross point WZ of the meniscus vibration can be obtained. It is thought that you can. Further, the second pulling pulse is set to be applied at a position of (3/4) × Tc, and is set to be applied at the maximum point WP on the ejection side of the meniscus vibration. It is thought that the effect of this can be obtained.

  In addition, if the timing (application start time) at which the two pulling pulses are applied is within a certain range from the above points, it is considered that the same effect can be obtained.

  Therefore, the first pulling pulse PP1 is applied within the range of (1/2) × Tc or more and (5/8) × Tc or less (the range A in FIGS. 4 and 5) after the application of the ejection pulse DP is started. The second pulling pulse PP2 is applied within the range of (3/4) × Tc or more and less than Tc (range B in FIGS. 4 and 5) after the application of the ejection pulse DP is started. It is set so that.

  An experiment was conducted to confirm the state of satellite generation when the application timing of the first pulling pulse PP1 was delayed.

  The first pulling pulse PP1 was applied while being shifted stepwise in a direction delayed from (1/2) × Tc, and the number of satellites generated was detected.

  FIG. 6 is a table showing experimental results.

  The Helmholtz period Tc of the droplet discharge head used in the experiment was 5 [μs], and the pulse width of the discharge pulse DP was 2.25 [μs].

  The application start time of the first pulling pulse PP1 is (1) 2.50 [(1/2) × Tc] [μs], (2) 2.81 [(9/16) × Tc] [μs], (3) 3.13 [(5/8) × Tc] [μs], (4) 3.44 [(11/16) × Tc] [μs], (5) 3.75 [(3/4) × Tc] [μs].

  From the experimental results, it was confirmed that no satellite was generated in the range of (1/2) × Tc to (5/8) × Tc.

  Note that the second pulling pulse PP2 accelerates the vibration of the meniscus moving in the pressure chamber direction, and therefore, within the range of (3/4) × Tc or more and less than Tc after the start of application of the ejection pulse DP. If it is set to be applied, substantially the same effect can be obtained. However, the closer to (3/4) × Tc, the earlier the action of cutting the droplets can be made, and the effect can be further enhanced.

  As described above, the drive signal W applied to the actuator 20 includes the first pulling pulse PP1 and the second pulling pulse PP2 in addition to the discharge pulse DP for discharging the droplet from the nozzle 14, and The application start point of the first pulling pulse is set within the range of (1/2) × Tc or more and (5/8) × Tc or less after the application of the ejection pulse DP, and the second pulling pulse PP2 By setting the application start point within the range of (3/4) × Tc or more and less than Tc after the start of application of the ejection pulse DP, it is possible to efficiently separate the droplets and effectively generate satellites. Can be suppressed.

  When the application timing of the first pulling pulse PP1 and the second pulling pulse PP2 is set based on the meniscus vibration when the discharge pulse DP is applied, the application start point of the first pulling pulse PP1 is the discharge start point. The meniscus vibration generated by applying the pulse DP can be set within a range of (1/8) × Tc from the time point when the zero crossing occurs, and the application start point of the second pulling pulse PP2 is the discharge pulse DP The application start point of the second pulling pulse PP2 can be set within a range of (1/4) × Tc from the time point at which the meniscus vibration generated by applying the voltage becomes maximum on the ejection side.

  As described above, the first pulling pulse PP1 is equal to the zero cross point WZ of the meniscus vibration generated by applying the ejection pulse DP, that is, (1/2) × Tc after the start of application of the ejection pulse DP. Most preferably, it is applied at the time. For this purpose, it is necessary to narrow the pulse width of the discharge pulse DP (the start point of the pressure chamber contraction element DP-3 of the discharge pulse DP needs to be advanced). On the other hand, when the pulse width of the ejection pulse DP is narrowed, the speed of the liquid droplet ejected from the nozzle 14 (droplet velocity) is decreased. Therefore, it is preferable to narrow the pulse width within a range in which the droplet speed is not slowed more than necessary, and it is preferably 5% to 15% narrower than (1/2) × Tc.

  FIG. 7 is a table showing the results of an experiment showing the droplet velocity and the satellite generation status when the ejection pulse DP is ejected while changing the pulse width.

  In the experiment, the pulse width of the ejection pulse DP is (1) 2.50 [μs], (2) 2.38 [μs], (3) 2.25 [μs], (4) 2.13 [μs], (5) The drop velocity and the number of satellites generated were detected as 2.00 [μs].

  The Helmholtz period Tc of the droplet discharge head used in the experiment was 5 [μs], and was discharged at a period of 25 [V] and 1 [kHz].

  From the experiment, if the rate of narrowing the pulse width is 5% or less of (1/2) × Tc, the satellite cannot be reduced. Conversely, if the rate of reducing the pulse width is 15% or more of (1/2) × Tc, It was confirmed that the speed was too slow.

  Therefore, in order to secure the desired droplet velocity while enhancing the satellite suppression effect, it is preferable to make the pulse width of the ejection pulse DP narrower by 5% to 15% than (1/2) × Tc.

<< Modification of drive signal >>
FIG. 8 is a waveform diagram showing a modified example of the drive signal for one droplet ejection period generated by the drive device.

  As shown in the figure, the drive signal W1 of this example is composed of one pulling pulse, and this is different from the drive signal W of the above-described embodiment. That is, the drive signal W1 of this example is composed of one ejection pulse DP and one pulling pulse PP.

  The ejection pulse DP is the same as the ejection pulse DP of the drive signal W in the above embodiment, and is a pulse for ejecting a predetermined amount of droplets from the nozzle 14. The pulse width of the ejection pulse DP is set to (1/2) × Tc.

  The pulling pulse PP is a pulse that draws the meniscus in a stepwise manner toward the pressure chamber, and is applied following the ejection pulse DP. The pulling pulse PP includes a first pressure chamber expansion element PP-1 that expands the pressure chamber 16 to the first volume, and a pressure chamber that is expanded to the first volume by the first pressure chamber expansion element PP-1. Maintenance element PP-2 for maintaining the volume of 16; second pressure chamber expansion element PP-3 for expanding the volume of the pressure chamber 16 from the first volume to the second volume; and pressure for contracting the pressure chamber 16 It is comprised with chamber contraction element PP-4.

  The first pressure chamber expansion element PP-1 has the same function as the pressure chamber expansion element PP1-1 of the first pulling pulse PP1 of the drive signal W in the above embodiment, and the second pressure chamber expansion element PP. -3 has the same function as the pressure chamber expansion element PP2-1 of the second pulling pulse PP2 of the drive signal W of the above embodiment.

  Therefore, the starting point of the first pressure chamber expansion element PP-1 is within the range of (1/2) × Tc or more and (5/8) × Tc or less after the start of application of the ejection pulse DP (the range of FIG. 8). A) and the start point of the second pressure chamber expansion element PP-3 is within the range of (3/4) × Tc or more and less than Tc after the start of application of the ejection pulse DP (range B in FIG. 8). Set to

  Alternatively, the starting point of the first pressure chamber expansion element PP-1 is set within a range of (1/8) × Tc from the time point WZ at which the meniscus vibration generated by applying the ejection pulse DP becomes zero cross. The application start point of the second pressure chamber expansion element PP-3 is within a range of (1/4) × Tc from the time point when the meniscus vibration generated by applying the discharge pulse DP becomes maximum on the discharge side. Is set.

  In the drive signal W1 shown in FIG. 8, the start point of the first pressure chamber expansion element PP-1 of the pull pulse PP is set to a point of (9/16) × Tc after the start of application of the discharge pulse DP, and the second The start point of the pressure chamber expansion element PP-3 is set to a point of (7/8) × Tc after the start of application of the ejection pulse DP.

  As described above, even when the pulling pulse PP is constituted by one pulse having the first pressure chamber expansion element PP-1 and the second pressure chamber expansion element PP-3, the same as the drive signal W of the above embodiment. An effect can be obtained.

  In this case as well, in order to increase the satellite suppression effect and secure a desired droplet velocity, the pulse width of the ejection pulse DP may be narrowed by 5% to 15% than (1/2) × Tc. preferable.

<< Other Embodiments >>
In the above embodiment, only one ejection pulse is incorporated in the drive signal, but a plurality of ejection pulses may be incorporated (for example, a plurality of ejection pulses are incorporated at a constant interval). In this case, the pulling pulse is incorporated after the final ejection pulse. Further, when adjusting the pulse width (when narrowing), it is performed only for the final ejection pulse.

  When incorporating a plurality of ejection pulses, the crest value may be set to gradually increase. As described above, when a plurality of ejection pulses are incorporated in the drive waveform during ink ejection, the peak value of each ejection pulse is set so as to gradually increase, so that the ink droplet ejected later becomes the ink droplet ejected earlier. It is possible to catch up with the media and land on the media in a single drop when landing. When the ejected ink droplets are landed in a single droplet state, the landed shape becomes clear, so that a higher quality image can be recorded.

  Further, when a plurality of ejection pulses are incorporated, the dot diameter of the ink droplets ejected onto the paper may be changed by changing the number of ejection pulses incorporated.

  FIG. 9 is a waveform showing an example of a drive signal when a plurality of ejection pulses having the same peak value (voltage) are incorporated within one droplet ejection cycle, and the dot diameter is changed by changing the number of ejection pulses incorporated. FIG. FIG. 6A shows a drive waveform when a small dot is ejected, FIG. 5B is a medium dot, and FIG.

  As shown in FIGS. 9A to 9C, the ejection pulses are incorporated at regular intervals. A small dot is incorporated by incorporating one, a medium dot is incorporated by incorporating two, and a large dot is formed by incorporating three. As described above, gradation recording can be performed by forming a plurality of types of dots having different sizes.

  In the drive signal of FIG. 9, the pulling pulse incorporated after the final ejection pulse is composed of two pulses, but the pulling pulse can be composed of one pulse (see FIG. 8).

<< Application example to inkjet recording apparatus >>
An ink jet recording apparatus to which the above-described liquid droplet ejection apparatus is applied will be described.

(Description of overall configuration of inkjet recording apparatus)
FIG. 10 is an overall configuration diagram of the ink jet recording apparatus. The ink jet recording apparatus 310 shown in the figure records a color image on a medium 314 that is a sheet using four color inks of magenta (M), black (K), cyan (C), and yellow (Y). This is a color printer.

  The ink jet recording apparatus 310 mainly includes a paper feeding unit 320, a processing liquid application unit 330, a drawing unit 340, a drying processing unit 350, a fixing processing unit 360, and a discharge unit 370. Intermediate transport drums 332, 342, 352, and 362 are provided as means for delivering the media 314 transported upstream of the processing liquid application unit 330, the drawing unit 340, the drying processing unit 350, and the fixing processing unit 360. Conveying drums 334, 344, 354, and 364 are provided as means for conveying while holding the media 314 in the coating unit 330, the drawing unit 340, the drying processing unit 350, and the fixing processing unit 360, respectively.

  The intermediate transport drums 332, 342, 352, 362 and the transport drums 334, 344, 354, 364 are provided with grippers 380A, 380B that hold the front end portion (or rear end portion) of the medium 314 at predetermined positions on the outer peripheral surface. It has been. The gripper 380A and the gripper 380B have the same structure for holding the leading end portion of the medium 314 and the structure for transferring the media 314 between the gripper provided on the other transport drum or the intermediate transport drum, and the gripper 380 </ b> A and gripper 380 </ b> B are arranged at symmetrical positions that are moved 180 ° in the rotation direction of the conveyance drum 334 on the outer peripheral surface of the conveyance drum 334.

  When the intermediate transport drums 332, 342, 352, 362 and the transport drums 334, 344, 354, 364 are rotated in a predetermined direction with the gripper 380A, 380B holding the leading end of the medium 314, the intermediate transport drum 332, The medium 314 is rotated and conveyed along the outer peripheral surfaces of 342, 352, and 362 and the conveying drums 334, 344, 354, and 364.

  In FIG. 10, only the grippers 380 </ b> A and 380 </ b> B provided on the transport drum 334 are denoted by reference numerals, and the grippers of other transport drums and intermediate transport drums are omitted.

  When the medium 314 stored in the paper feeding unit 320 is fed to the processing liquid application unit 330, the aggregation processing liquid (hereinafter simply referred to as “processing”) is formed on the recording surface of the medium 314 held on the outer peripheral surface of the transport drum 334. May be described as “Liquid”.). The “recording surface of the medium 314” is an outer surface in a state where the conveyance drums 334, 344, 354, and 364 are held, and is a surface opposite to a surface held by the conveyance drums 334, 344, 354, and 364. is there.

  Thereafter, the medium 314 to which the aggregation processing liquid has been applied is sent out to the drawing unit 340, and color ink is applied to the area of the recording surface to which the aggregation processing liquid has been applied, thereby forming a desired image.

  Further, the medium 314 on which the image of the color ink is formed is sent to the drying processing unit 350, where the drying processing unit 350 performs drying processing, and after the drying processing, the media 314 is sent to the fixing processing unit 360 to perform fixing processing. Is done. By performing the drying process and the fixing process, the image formed on the medium 314 is hardened. In this manner, a desired image is formed on the recording surface of the medium 314. After the image is fixed on the recording surface of the medium 314, the image is conveyed from the discharge unit 370 to the outside of the apparatus.

  Hereinafter, each part (the paper feed unit 320, the processing liquid application unit 330, the drawing unit 340, the drying processing unit 350, the fixing processing unit 360, and the discharge unit 370) of the ink jet recording apparatus 310 will be described in detail.

(Paper Feeder)
The paper feed unit 320 is provided with a paper feed tray 322 and a feed mechanism (not shown), and the media 314 is configured to be fed from the paper feed tray 322 one by one. The medium 314 sent out from the paper feed tray 322 is positioned by a guide member (not shown) so that the front end is positioned at a gripper (not shown) of the intermediate transport drum (feed drum) 332 and temporarily stops.

(Processing liquid application part)
The treatment liquid application unit 330 holds the medium 314 delivered from the paper supply drum 332 on the outer peripheral surface and conveys the medium 314 in a predetermined conveyance direction (treatment liquid drum) 334, and the treatment liquid drum 334. And a treatment liquid coating device 336 that applies a treatment liquid to the recording surface of the medium 314 held on the outer peripheral surface. When the processing liquid drum 334 is rotated counterclockwise in FIG. 10, the media 314 is rotated and conveyed in the counterclockwise direction along the outer peripheral surface of the processing liquid drum 334.

  The processing liquid coating device 336 shown in FIG. 10 is provided at a position facing the outer peripheral surface (media holding surface) of the processing liquid drum 334. As a configuration example of the processing liquid coating device 336, a processing liquid container in which the processing liquid is stored, a pumping roller that is partially immersed in the processing liquid in the processing liquid container, and pumps up the processing liquid in the processing liquid container, and a pumping roller An embodiment including an application roller (rubber roller) that moves the pumped processing liquid onto the medium 314 is exemplified.

  In addition, there is an aspect in which a coating roller moving mechanism that moves the coating roller in the vertical direction (normal direction of the outer peripheral surface of the treatment liquid drum 334) is provided, and the collision between the coating roller and the grippers 380A and 380B can be avoided. preferable.

  The treatment liquid applied to the medium 314 by the treatment liquid application unit 330 contains a color material aggregating agent that aggregates the color material (pigment) in the ink applied by the drawing unit 340, and the treatment liquid and the ink on the medium 314. Contact with the ink promotes separation of the colorant and the solvent in the ink.

  The treatment liquid application device 336 is preferably applied while measuring the amount of the treatment liquid to be applied to the medium 314. The film thickness of the treatment liquid on the medium 314 is the diameter of the ink droplet ejected from the drawing unit 340. It is preferable to make it sufficiently smaller.

(Drawing part)
The drawing unit 340 includes a conveyance drum (drawing drum) 344 that holds and conveys the medium 314, a sheet suppression roller 346 for bringing the medium 314 into close contact with the drawing drum 344, and an inkjet head (liquid) that applies ink to the medium 314. Droplet discharge heads) 348M, 348K, 348C, 348Y. The basic structure of the drawing drum 344 is the same as that of the processing liquid drum 334 described above, and a description thereof is omitted here.

  The sheet pressing roller 346 is a guide member for bringing the medium 314 into close contact with the outer peripheral surface of the drawing drum 344, faces the outer peripheral surface of the drawing drum 344, and the delivery position of the medium 314 between the intermediate conveyance drum 342 and the drawing drum 344 It is disposed downstream of the medium 314 in the transport direction and upstream of the ink jet heads 348M, 348K, 348C, and 348Y in the transport direction of the medium 314.

  The medium 314 transferred from the intermediate transport drum 342 to the drawing drum 344 is pressed by the sheet pressing roller 346 when being rotated and transported with the leading end held by a gripper (not shown), and the outer periphery of the drawing drum 344 Adhere to the surface. In this way, after the medium 314 is brought into close contact with the outer peripheral surface of the drawing drum 344, the medium 314 is sent to the print area immediately below the inkjet heads 348M, 348K, 348C, 348Y without being lifted from the outer peripheral surface of the drawing drum 344. .

  The inkjet heads 348M, 348K, 348C, and 348Y correspond to inks of four colors, magenta (M), black (K), cyan (C), and yellow (Y), respectively, and the rotation direction of the drawing drum 344 (see FIG. 10 in the counterclockwise direction), and the nozzle surfaces (ink ejection surfaces) of the inkjet heads 348M, 348K, 348C, and 348Y face the recording surface of the medium 314 held on the drawing drum 344. Are arranged as follows.

  Further, in the inkjet heads 348M, 348K, 348C, and 348Y shown in FIG. 10, the recording surface of the medium 314 held on the outer peripheral surface of the drawing drum 344 and the nozzle surfaces of the inkjet heads 348M, 348K, 348C, and 348Y are substantially parallel. As shown in FIG.

  The inkjet heads 348M, 348K, 348C, and 348Y are full-line heads having a length corresponding to the maximum width of the image forming area in the medium 314 (the length in the direction orthogonal to the conveyance direction of the medium 314). It is fixedly installed so as to extend in a direction orthogonal to the conveyance direction 314.

  On the nozzle surfaces of the inkjet heads 348M, 348K, 348C, and 348Y, nozzles for discharging ink are formed in a matrix arrangement over the entire width of the image forming area of the medium 314.

  When the media 314 is transported to the print area immediately below the inkjet heads 348M, 348K, 348C, 348Y, based on the image data, the areas where the aggregation processing liquid of the media 314 is applied from the inkjet heads 348M, 348K, 348C, 348Y. Each color ink is ejected.

  When the droplets of the corresponding color ink are ejected from the inkjet heads 348M, 348K, 348C, 348Y toward the recording surface of the medium 314 held on the outer peripheral surface of the drawing drum 344, the processing liquid and Aggregation reaction of the color material (pigment-based color material) dispersed in the ink or the insoluble color material (dye-based color material) is brought into contact with the ink, and the color material aggregate is formed. As a result, movement of the color material (dot misalignment, dot color unevenness) in the image formed on the medium 314 is prevented.

  In addition, since the drawing drum 344 of the drawing unit 340 is structurally separated from the processing liquid drum 334 of the processing liquid application unit 330, the processing liquid does not adhere to the inkjet heads 348M, 348K, 348C, and 348Y. In addition, the cause of abnormal ink ejection can be reduced.

  In this example, the configuration of CMYK standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, and special colors are used as necessary. Ink may be added. For example, it is possible to add an ink jet head that discharges light ink such as light cyan and light magenta, and the arrangement order of the color heads is not particularly limited.

(Dry processing part)
The drying processing unit 350 includes a conveyance drum (drying drum) 354 that holds and conveys the medium 314 after image formation, and a solvent drying device 356 that performs a drying process for evaporating moisture (liquid component) on the medium 314. ing. The basic structure of the drying drum 354 is the same as that of the processing liquid drum 334 and the drawing drum 344 described above, and a description thereof is omitted here.

  The solvent drying device 356 is a processing unit that is disposed at a position facing the outer peripheral surface of the drying drum 354 and evaporates moisture present in the medium 314. When ink is applied to the medium 314 by the drawing unit 340, the liquid component (solvent component) of the ink separated by the aggregation reaction between the treatment liquid and the ink and the liquid component (solvent component) of the treatment liquid remain on the medium 314. Therefore, it is necessary to remove such a liquid component.

  The solvent drying device 356 is a processing unit for removing the liquid component on the medium 314 by performing a drying process for evaporating the liquid component existing on the medium 314 by using heating by a heater, blowing by a fan, or a combination thereof. is there. The amount of heating and the amount of air supplied to the medium 314 are appropriately set according to parameters such as the amount of moisture remaining on the medium 314, the type of the medium 314, and the conveyance speed (interference processing time) of the medium 314.

  When the drying process by the solvent drying device 356 is performed, the drying drum 354 of the drying processing unit 350 is structurally separated from the drawing drum 344 of the drawing unit 340, so that the inkjet heads 348M, 348K, 348C, and 348Y. In this case, it is possible to reduce the cause of abnormal ink ejection due to drying of the head meniscus by heat or air blowing.

  In order to exhibit the effect of correcting cockling of the media 314, the curvature of the drying drum 354 is preferably 0.002 (1 / mm) or more. In order to prevent the curling of the media after the drying process, the curvature of the drying drum 354 is preferably 0.0033 (1 / mm) or less.

  In addition, a means (for example, a built-in heater) for adjusting the surface temperature of the drying drum 354 may be provided, and the surface temperature may be adjusted to 50 ° C. or higher. By performing heat treatment from the back surface of the media 314, drying is promoted, and image destruction during the subsequent fixing process is prevented. In this aspect, it is more effective to provide means for bringing the media 314 into close contact with the outer peripheral surface of the drying drum 354. As an example of means for bringing the medium 314 into close contact, vacuum adsorption, electrostatic adsorption, and the like can be given.

  The upper limit of the surface temperature of the drying drum 354 is not particularly limited, but from the viewpoint of safety of maintenance work such as cleaning ink adhering to the surface of the drying drum 354 (preventing burns due to high temperatures). It is preferably set to 75 ° C. or lower (more preferably 60 ° C. or lower).

  Holding and rotating on the outer peripheral surface of the drying drum 354 thus configured so that the recording surface of the medium 314 faces outward (that is, in a state where the recording surface of the medium 314 is convex). By performing the drying process while being conveyed, drying unevenness due to wrinkling or floating of the media 314 is surely prevented.

(Fixing processing part)
The fixing processing unit 360 holds a conveyance drum (fixing drum) 364 that holds and conveys the medium 314, a heater 366 that heats the medium 314 on which an image is formed and from which the liquid is removed, and the medium 314. And a fixing roller 368 for pressing from the recording surface side. The basic structure of the fixing drum 364 is the same as that of the processing liquid drum 334, the drawing drum 344, and the drying drum 354, and a description thereof is omitted here. The heater 366 and the fixing roller 368 are disposed at positions facing the outer peripheral surface of the fixing drum 364, and are sequentially disposed from the upstream side in the rotation direction of the fixing drum 364 (counterclockwise direction in FIG. 10).

  In the fixing processing unit 360, the recording surface of the medium 314 is subjected to preheating processing by the heater 366 and fixing processing by the fixing roller 368. The heating temperature of the heater 366 is appropriately set according to the type of media, the type of ink (the type of polymer fine particles contained in the ink), and the like. For example, a mode in which the glass transition point temperature or the minimum film forming temperature of the polymer fine particles contained in the ink is considered.

 The fixing roller 368 is a roller member that heats and pressurizes the dried ink to weld the self-dispersing polymer fine particles in the ink to form a film of the ink, and is configured to heat and press the medium 314. . Specifically, the fixing roller 368 is disposed so as to be in pressure contact with the fixing drum 364 and constitutes a nip roller with the fixing drum 364. As a result, the medium 314 is sandwiched between the fixing roller 368 and the fixing drum 364 and nipped at a predetermined nip pressure, and the fixing process is performed.

 As an example of the configuration of the fixing roller 368, there is an embodiment in which the fixing roller 368 is configured by a heating roller in which a halogen lamp is incorporated in a metal pipe such as aluminum having good thermal conductivity. By heating the media 314 with such a heating roller, when thermal energy equal to or higher than the glass transition temperature of the polymer fine particles contained in the ink is applied, the polymer fine particles melt and a transparent film is formed on the surface of the image. The

  When pressure is applied to the recording surface of the medium 314 in this state, the polymer fine particles melted into the unevenness of the medium 314 are pressed and fixed, and the unevenness of the image surface is leveled, so that preferable glossiness can be obtained. A configuration in which a plurality of fixing rollers 368 are provided in accordance with the thickness of the image layer and the glass transition temperature characteristics of the polymer particles is also preferable.

  The surface hardness of the fixing roller 368 is preferably 71 ° or less. By making the surface of the fixing roller 368 softer, a tracking effect can be expected with respect to the unevenness of the media 314 caused by cockling, and fixing unevenness due to the unevenness of the media 314 is more effectively prevented.

  In the ink jet recording apparatus 310 shown in FIG. 10, an inline sensor 382 is provided at the subsequent stage (downstream side in the medium transport direction) of the processing area of the fixing processing unit 360. The inline sensor 382 is a sensor for reading an image formed on the medium 314 (or a check pattern formed in a blank area of the medium 314), and a CCD (Charged Coupled Device) line sensor is preferably used.

  In the ink jet recording apparatus 310 shown in this example, the presence or absence of ejection abnormality of the ink jet heads 348M, 348K, 348C, and 348Y is determined based on the reading result of the inline sensor 382 (details will be described later). Further, the inline sensor 382 may include a measuring unit for measuring a moisture amount, a surface temperature, a glossiness, and the like. In such an embodiment, parameters such as the processing temperature of the drying processing unit 350, the heating temperature of the fixing processing unit 360, and the pressurizing pressure are appropriately adjusted based on the moisture content, surface temperature, and gloss reading result, and the temperature inside the apparatus. The control parameter is adjusted as appropriate in accordance with the change and the temperature change of each part.

(Discharge part)
As shown in FIG. 10, a discharge unit 370 is provided following the fixing processing unit 360. The discharge unit 370 includes an endless conveyance belt 374 wound around the stretching rollers 372A and 372B, and a discharge tray 376 that stores the media 314 after image formation.

  The medium 314 after the fixing process sent out from the fixing processing unit 360 is transported by the transport belt 374 and discharged to the discharge tray 376.

(Description of structure of inkjet head)
FIG. 11 is a schematic configuration diagram of the ink jet head, which is a diagram (a plan perspective view of the head) of the recording surface of the medium as viewed from the ink jet head. In addition, since the inkjet heads 348M, 348K, 348C, and 348Y of the respective colors have the same structure, in the following description, the inkjet heads 348M, 348K, 348C, and 348Y are collectively referred to when it is not necessary to distinguish them. Will be referred to as “inkjet head 348”.

  The ink jet head 348 shown in the figure forms a multi-head by connecting n head modules 348-i (i is an integer from 1 to n) in a line. Each head module 348-i is supported by head covers 349A and 349B from both sides of the inkjet head 348 in the short direction. It is also possible to configure a multi-head by arranging the head modules 348 in a staggered manner.

  As an application example of a multi-head configured by a plurality of head modules, a full-line head corresponding to the full width of a medium can be given. In the full-line head, a plurality of nozzles are arranged along the direction (main scanning direction) perpendicular to the moving direction (sub-scanning direction) of the medium, corresponding to the length (width) in the main scanning direction of the medium. Have a structure. An image can be formed on the entire surface of the medium by a so-called single-pass image recording method in which the ink jet head 348 having such a structure and the medium are scanned only once relatively to perform image recording.

  FIG. 12 is a partially enlarged view of the inkjet head. As shown in the figure, the head module 348 has a substantially parallelogram planar shape, and an overlap portion is provided between adjacent head modules. The overlap portion is a connecting portion of the head modules, and nozzles that belong to head modules having different dots adjacent to the head module 348-i in the arrangement direction (the horizontal direction in FIG. 11, the main scanning direction X shown in FIG. 13). Formed by.

  FIG. 13 is a plan view showing the nozzle arrangement of the head module 348-i. As shown in the figure, each head module 348-i has a structure in which nozzles 328 are arranged two-dimensionally, and a head including such a head module 348-i is a so-called matrix head. .

  The head module 348-i shown in FIG. 13 has a large number of nozzles 328 along a column direction W that forms an angle α with respect to the sub-scanning direction Y and a row direction V that forms an angle β with respect to the main scanning direction X. It has an aligned structure, and the substantial nozzle arrangement density in the main scanning direction X is increased. In FIG. 13, nozzle groups (nozzle rows) arranged along the row direction V are denoted by reference numeral 328V, and nozzle groups (nozzle rows) arranged along the column direction W are denoted by reference numeral 328W. ing.

  In this matrix arrangement, when the interval between adjacent nozzles in the sub-scanning direction is Ls, in the main scanning direction, each nozzle 328 is substantially equivalent to a linear arrangement with a constant pitch P = Ls / tan θ. It can be handled.

  A pressure chamber is provided for each nozzle 328 inside the inkjet head 348. Each pressure chamber is provided with a piezoelectric element as an actuator. By driving the piezoelectric element (applying a drive signal), the pressure chamber expands / contracts, and an ink droplet is ejected from the nozzle 328.

(Description of control system)
FIG. 14 is a block diagram showing a system configuration of a control system of the ink jet recording apparatus. As shown in FIG. 14, the inkjet recording apparatus 310 includes a communication interface 440 and a system control unit 442, and overall control of each unit of the apparatus is performed by the system control unit 442.

  The communication interface 440 is an interface unit (image input unit) that receives image data sent from the host computer 454. As the communication interface 440, a serial interface such as USB (Universal Serial Bus), Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  The system control unit 442 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 310 according to a predetermined program and performs various calculations. Functions as an arithmetic unit. In addition, it generates control signals for controlling the conveyance control unit 444, the image processing unit 446, the head driving unit 448, and the like, and functions as a memory controller for the image memory 450 and a ROM (Read Only Memory) 452.

  The image processing unit 446 is a processing block that performs predetermined processing on the image data, and includes a processor having an image processing function. Image data sent from the host computer 454 is taken into the inkjet recording apparatus 310 via the communication interface 440 and temporarily stored in the image memory 450. The image memory 450 is a storage unit that stores an image input via the communication interface 440, and data is read and written through the system control unit 442. The image memory 450 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The image memory 450 stores programs executed by the CPU of the system control unit 442 and various data necessary for control (including data for ejecting test charts, abnormal nozzle information, and the like). The image memory 450 may be a non-rewritable storage unit or a rewritable storage unit such as a flash memory.

  A temporary storage unit (not shown) is used as a temporary storage area for image data and various data, and is also used as a program development area and a calculation work area for the CPU.

  The image processing unit 446 performs various signal processing on the image data (multi-valued input image data) in the image memory under the control of the system control unit 442 to generate dot placement data for droplet ejection control (described above). This corresponds to the image processing apparatus 100 of the liquid droplet ejection apparatus 1.

  The image processing unit 446 includes functional blocks such as a density data generation unit, a correction processing unit, and a dot arrangement data generation unit. Each of these functional blocks can be realized by ASIC (Application Specific Integrated Circuit), software, or an appropriate combination.

  The density data generation unit is a signal processing unit that generates initial density data for each ink color from input image data, and includes density conversion processing (including UCR (Under Color Removal) processing and color conversion) and when necessary. Performs a pixel number conversion process. The correction processing unit is a processing unit that performs density correction using the density correction coefficient, and performs unevenness correction processing.

  The dot arrangement data generation unit is a signal processing unit including a halftoning processing unit that converts the corrected image data (density data) generated by the correction processing unit into binary or multi-value dot arrangement data. (Multi-value) processing is performed. 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. In the halftone process, generally, gradation image data having an M value (M ≧ 3) is converted into binary or multi-value gradation image data smaller than M. In the simplest example, the data is converted into binary (dot on / off) dot arrangement data. However, in halftone processing, the dot size type (for example, large size, medium size, small size) is used as in the above embodiment. Multi-level quantization corresponding to three types such as size can be performed.

  The image processing unit 446 is provided with an image buffer memory (not shown), and image data, parameters, and other data are temporarily stored in the image buffer memory when the image processing unit 446 processes image data. Note that the image buffer memory may be attached to the image processing unit 446 or may be used as the image memory. Further, the image processing unit 446 may be integrated with the system control unit 442 and configured with one processor.

  The dot arrangement data generated by the image processing unit 446 is given to the head driving unit 448, and the ink ejection operation of the inkjet head 348 is controlled.

  The head drive unit 448 functions as a drive signal generation unit that generates a drive signal for driving an actuator corresponding to each nozzle 328 of the inkjet head 348 (corresponding to the drive device 200 of the droplet discharge device 1 in FIG. 1). .)

  An overview of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 440 and stored in an image memory. At this stage, for example, RGB multivalued image data is stored in the image memory.

  In the ink jet recording apparatus 310, a pseudo continuous tone image is formed by changing the droplet ejection density and dot size of fine dots with ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the image memory is sent to the image processing unit 446 via the system control unit 442, and is processed by the density data generation unit, the correction processing unit, and the dot arrangement data generation unit. It is converted into dot arrangement data for each ink color.

  That is, the image processing unit 446 performs processing for converting the input RGB image data into dot data of M, K, C, and Y colors. The dot arrangement data thus generated by the image processing unit 446 is stored in the image buffer memory. This dot data for each color is converted into MKCY droplet ejection data for ejecting ink from the nozzles of the inkjet head 348 and printed, dot arrangement data (dot timing for each nozzle and the dot size at each drive timing ( Discharge amount)) is confirmed.

  The head drive unit 448 outputs a drive signal for driving an actuator corresponding to each nozzle 328 of the inkjet head 348 based on the print content based on the dot arrangement data. The head drive unit 448 may include a feedback control system for keeping the head drive conditions constant.

  In this way, the drive signal output from the head drive unit 448 is applied to the inkjet head 348, whereby ink is ejected from the corresponding nozzle 328. An image is formed on the medium 314 by controlling ink ejection from the inkjet head 348 in synchronization with the conveyance speed of the medium 314.

  As described above, the ejection amount and ejection timing of ink droplets from each nozzle are controlled via the head drive unit 448 based on the dot arrangement data generated through the required signal processing in the image processing unit 446. . Thereby, a desired dot size and dot arrangement are realized.

  The in-line detection unit 470 illustrated in FIG. 14 is a functional block that provides information regarding abnormal nozzles to the system control unit 442 through reading of nozzle detection patterns, processing of read data, and processing of determining abnormal nozzles. The inline detection unit 470 includes the inline sensor 382 illustrated in FIG.

  The system control unit 442 performs various corrections on the ink jet head 348 based on information on the abnormal nozzle obtained from the inline detection unit 470 and other information, and also performs cleaning operations such as preliminary ejection, suction, and wiping as necessary ( Nozzle recovery operation) is performed.

  Although not shown, a maintenance processing unit including members necessary for head maintenance such as an ink receiver, a suction cap, a suction pump, and a wiper blade is provided as means for executing the cleaning operation.

  In addition, an operation unit as a user interface is provided, and the operation unit includes an input device 468 and a display unit (display) 466 for an operator (user) to perform various inputs. The input device 468 can employ various forms such as a keyboard, a mouse, a touch panel, and buttons. By operating the input device 468, the operator can input printing conditions, select an image quality mode, input / edit attached information, search for information, etc. This can be confirmed through display on the display unit 466. The display unit 466 also functions as means for displaying a warning such as an error message.

  The inkjet recording apparatus 310 of this example has a plurality of image quality modes, and the image quality mode is set by a user's selection operation or by automatic selection by a program. The criterion for determining an abnormal nozzle is changed according to the output image quality level required in the set image quality mode. The higher the required quality, the more severe the criteria.

  Information relating to printing conditions in each image quality mode and abnormal nozzle determination criteria is stored in the image memory 450.

[Example of application to other devices]
In the above embodiment, application to an inkjet recording apparatus that performs color printing on a sheet of paper has been described as an example, but the scope of application of the present invention is not limited to this example. For example, a wiring drawing device for drawing a wiring pattern of an electronic circuit, a manufacturing device for various devices, a resist printing device using a resin liquid as a functional liquid for ejection, a color filter manufacturing device, and a fine material using a material for material deposition The present invention can be widely applied to a droplet discharge device that forms various shapes and patterns by ejecting droplets, such as a fine structure forming device that forms structures.

  DESCRIPTION OF SYMBOLS 1 ... Droplet discharge apparatus, 10 ... Droplet discharge head, 12 ... Nozzle surface, 14 ... Nozzle, 16 ... Pressure chamber, 18 ... Vibration plate, 20 ... Actuator, 22 ... Supply port, 24 ... Collection port, 26 ... Common Supply flow path 28... Common recovery flow path 30. Individual supply flow path 32. Individual recovery flow path 100 100 Image processing apparatus 200 Drive apparatus 310 Inkjet recording apparatus 314 Media 320 , 322... Paper feed tray, 328... Nozzle, 330... Processing liquid coating unit, 332... Feeding drum, 334... Processing liquid drum, 336. ... Drawing drum, 346 ... Paper holding roller, 348 (348M, 348K, 348C, 348Y) ... Inkjet head, 349A, 349B ... Head cover, 350 ... Dry processing section 352: Intermediate transport drum, 354 ... Drying drum, 356 ... Solvent drying device, 360 ... Fixing processing unit, 362 ... Intermediate transport drum, 364 ... Fixing drum, 366 ... Heater, 368 ... Fixing roller, 370 ... Discharge unit, 372A, 372B ... tension roller, 354 ... conveyor belt, 376 ... discharge tray, 380A, 380B ... gripper, 440 ... communication interface, 442 ... system controller, 444 ... conveyor controller, 446 ... image processor, 448 ... head driver , 450 ... Image memory, 452 ... ROM, 454 ... Host computer, 466 ... Display unit, 468 ... Input device, 470 ... Inline detection unit, DP ... Discharge pulse, DP-1 ... Pressure chamber expansion element of discharge pulse, DP- 2 ... Discharge pulse maintenance element, DP-3 ... Discharge pulse pressure chamber contraction element, PP ... Pull pulse , PP-1 ... the first pressure chamber expansion element of the pull pulse, PP-2 ... the maintenance element of the pull pulse, PP-3 ... the second pressure chamber expansion element of the pull pulse, PP-4 ... the pressure chamber of the pull pulse Contraction element, PP1... First pulling pulse, PP1-1... Pressure chamber expansion element of first pulling pulse, PP1-2... First pulling pulse maintaining element, PP1. Chamber contraction element, PP2 ... second pull pulse, PP2-1 ... pressure chamber expansion element of second pull pulse, PP2-2 ... second pull pulse maintenance element, PP2-3 ... second pull pulse Pressure chamber contraction element, W ... drive signal, W1 ... drive signal, WP ... maximum point on the discharge side of meniscus vibration, WZ ... zero cross point of meniscus vibration

Claims (16)

A droplet discharge head having a nozzle, a pressure chamber communicating with the nozzle, and an actuator for expanding / contracting the pressure chamber;
A drive signal generator for generating a drive signal to be applied to the actuator;
With
The drive signal generated by the drive signal generator is
At least one ejection pulse for ejecting droplets from the nozzle;
A first pulling pulse that is applied after applying the final ejection pulse and draws the meniscus toward the pressure chamber;
A second pulling pulse that is applied after applying the first pulling pulse and pulls the meniscus toward the pressure chamber;
Including
When the Helmholtz period obtained from the structure of the droplet discharge head is Tc,
The ejection pulse width is set to (1/2) × Tc or less;
The application start point of the first pulling pulse is set within a range of (1/8) × Tc from the time when the meniscus vibration generated by applying the ejection pulse becomes zero crossing,
A droplet in which the application start point of the second pulling pulse is set within a range of (1/4) × Tc from the point in time at which the meniscus vibration generated by applying the discharge pulse becomes maximum on the discharge side Discharge device.   2. The droplet discharge device according to claim 1, wherein a width of the final discharge pulse is set to be 5% to 15% narrower than (1/2) × Tc.   The liquid droplet ejection apparatus according to claim 2, wherein the application start point of the first pulling pulse is set to a point where meniscus vibration generated by applying the ejection pulse becomes zero cross.   The droplet discharge device according to claim 3, wherein the application start point of the second pulling pulse is set to a point where meniscus vibration generated by applying the discharge pulse becomes maximum on the discharge side. A droplet discharge head having a nozzle, a pressure chamber communicating with the nozzle, and an actuator for expanding / contracting the pressure chamber;
A drive signal generator for generating a drive signal to be applied to the actuator;
With
The drive signal generated by the drive signal generator is
At least one ejection pulse for ejecting droplets from the nozzle;
A first pulling pulse that is applied after applying the final ejection pulse and draws the meniscus toward the pressure chamber;
A second pulling pulse that is applied after applying the first pulling pulse and pulls the meniscus toward the pressure chamber;
Including
When the Helmholtz period obtained from the structure of the droplet discharge head is Tc,
The ejection pulse width is set to (1/2) × Tc or less;
The application start point of the first pulling pulse is set within the range of (1/2) × Tc or more and (5/8) × Tc or less after the final application of the ejection pulse,
A droplet discharge device in which the application start point of the second pulling pulse is set within a range of (3/4) × Tc or more and less than Tc after the start of application of the final discharge pulse.   6. The liquid droplet ejection apparatus according to claim 5, wherein a width of the final ejection pulse is set to be 5% to 15% narrower than (1/2) × Tc.   The liquid droplet ejection apparatus according to claim 6, wherein the application start point of the first pulling pulse is set to a point of (½) × Tc after the application start of the final ejection pulse.   The liquid droplet ejection apparatus according to claim 7, wherein the application start point of the second pulling pulse is set to a point of (3/4) × Tc after the application start of the final ejection pulse. A droplet discharge head having a nozzle, a pressure chamber communicating with the nozzle, and an actuator for expanding / contracting the pressure chamber;
A drive signal generator for generating a drive signal to be applied to the actuator;
With
The drive signal generated by the drive signal generator is
At least one ejection pulse for ejecting droplets from the nozzle;
A first pressure chamber expansion element that expands the pressure chamber to a first volume; and a maintenance element that maintains the volume of the pressure chamber expanded to the first volume by the first pressure chamber expansion element; The pressure chamber includes a second pressure chamber expansion element that expands the volume of the pressure chamber from the first volume to the second volume, and a pressure chamber contraction element that contracts the pressure chamber, and the final ejection pulse is applied. A pulling pulse that is applied later to pull the meniscus stepwise into the pressure chamber;
Including
When the Helmholtz period obtained from the structure of the droplet discharge head is Tc,
A width of the ejection pulse is set to 1/2 Tc or less;
The starting point of the first pressure chamber expansion element is set within a range of (1/8) × Tc from the time point when the meniscus vibration generated by applying the ejection pulse becomes zero cross,
A liquid in which the starting point of the second pressure chamber expansion element is set within a range of (1/4) × Tc from the point in time at which the meniscus vibration generated by applying the discharge pulse becomes maximum on the discharge side Drop ejection device.   The droplet discharge device according to claim 9, wherein the width of the discharge pulse is set to be 5% to 15% narrower than (1/2) × Tc.   11. The droplet discharge device according to claim 10, wherein a start point of the first pressure chamber expansion element is set to a point where meniscus vibration generated by applying the discharge pulse becomes zero cross.   12. The droplet discharge device according to claim 11, wherein the start point of the second pressure chamber expansion element is set to a point at which meniscus vibration generated by applying the discharge pulse is maximized on the discharge side. A droplet discharge head having a nozzle, a pressure chamber communicating with the nozzle, and an actuator for expanding / contracting the pressure chamber;
A drive signal generator for generating a drive signal to be applied to the actuator;
With
The drive signal generated by the drive signal generator is
At least one ejection pulse for ejecting droplets from the nozzle;
A first pressure chamber expansion element that expands the pressure chamber to a first volume; and a maintenance element that maintains the volume of the pressure chamber expanded to the first volume by the first pressure chamber expansion element; The pressure chamber includes a second pressure chamber expansion element that expands the volume of the pressure chamber from the first volume to the second volume, and a pressure chamber contraction element that contracts the pressure chamber, and the final ejection pulse is applied. A pulling pulse that is applied later to pull the meniscus stepwise into the pressure chamber;
Including
When the Helmholtz period obtained from the structure of the droplet discharge head is Tc,
A width of the ejection pulse is set to 1/2 Tc or less;
The starting point of the first pressure chamber expansion element is set within a range of (1/2) × Tc or more and (5/8) × Tc or less after the final application of the ejection pulse,
A droplet discharge device in which a start point of the second pressure chamber expansion element is set within a range of (3/4) × Tc or more and less than Tc after the start of application of the final discharge pulse.   14. The droplet discharge device according to claim 13, wherein the width of the discharge pulse is set to be 5% to 15% narrower than (1/2) × Tc.   The droplet discharge device according to claim 14, wherein a start point of the first pressure chamber expansion element is set to a point of (½) × Tc after the start of application of the final discharge pulse.   The liquid droplet ejection apparatus according to claim 15, wherein a start point of the second pressure chamber expansion element is set to a point of (3/4) × Tc after the final application of the ejection pulse.

Images