JP2007229960A - Liquid droplet discharge device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily separate a liquid droplet from a liquid column, in case the liquid droplet is discharged by draw/squeeze control. <P>SOLUTION: This liquid droplet discharge device discharges the liquid droplet by ejecting the liquid column 80 from a nozzle 51 through drawing/squeezing liquid inside the nozzle 51 using a specified actuator, and at the same time, separating the liquid droplet from the liquid column 80. In this device, the device comprises a drive means which gives a drive waveform for liquid droplet discharge to the actuator each time the liquid droplet is discharged, a temperature variable element 31 which is housed in the inner wall of the nozzle 51 and gives temperature change to the liquid, and a temperature distribution setting means which sets temperature distribution inside the liquid column 80 using the temperature-variable element 31. The temperature distribution setting means sets the temperature of a part 81 located near the inner wall of the nozzle 51 lower than that of a constricted part 82 of the liquid column 80 by giving an input signal corresponding to the drive waveform for liquid droplet discharge, to the temperature-variable element 31. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a droplet discharge device, and more particularly to a droplet discharge device that discharges droplets by pulling control of a meniscus.

  As a method for ejecting droplets, so-called meniscus pulling control is known. Specifically, the meniscus (liquid level) in the nozzle is once retracted by pulling (pulling), the liquid in the nozzle is given a speed in the ejection direction by pushing (pushing), and the liquid column protrudes from the nozzle. The liquid droplets are separated from the liquid column by reducing the velocity of the liquid inside. The liquid droplets separated from the liquid column in this manner land on a medium to be ejected such as paper.

On the other hand, Patent Document 1 describes a piston that instantaneously pressurizes liquid so that the meniscus expands, and a heater that separates droplets from the expanded meniscus is provided around the nozzle. Yes.
JP 2000-238267 A (FIGS. 3 to 7)

  There is a demand for discharging minute droplets. In order to meet such demands, a method of discharging droplets by meniscus pulling control is suitable. In the pulling control, a liquid column having a diameter smaller than the nozzle diameter grows, and fine droplets can be separated from the liquid column.

  Moreover, it is required to discharge a highly viscous liquid. In a high-viscosity liquid, the aspect ratio between the diameter and length of the liquid column is large, and generally many satellite droplets are generated. This is because it becomes difficult to separate the main droplets as compared with a low-viscosity liquid.

  In the device described in Patent Document 1, a meniscus is expanded by a piston, and a droplet is separated from the expanded meniscus by a heater around the nozzle. Therefore, in general, a droplet having a diameter larger than the nozzle diameter is used. Will separate from the meniscus.

  By the way, in a droplet discharge apparatus that discharges droplets by pulling and controlling the meniscus, if a heater is provided around the nozzle, it is actually difficult to separate the droplets as follows.

  As shown in FIG. 9, in the pulling control, the diameter of the liquid column 90 protruding from the nozzle surface 50 a is smaller than the diameter of the nozzle 51, and the liquid in the nozzle 51 is heated by the heater 31 provided on the inner wall of the nozzle 51. As a result, the temperature of the portion 91 (near the inner wall of the nozzle) located near the inner wall of the nozzle 50 clipping the liquid column 90 is higher than the temperature of the portion 92 (necked portion) that should be constricted in the liquid column 90. Becomes higher. Therefore, so-called Marangoni convection is generated from the nozzle inner wall vicinity portion 91 toward the constricted portion 92. As a result, the formation of the constricted shape (concave shape) is delayed, and the separation of the droplets becomes difficult.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a droplet discharge device that can easily separate a droplet from a liquid column when the droplet is discharged by pulling control.

  In order to achieve the above-mentioned object, the invention according to claim 1 is characterized in that a liquid column is projected from the droplet discharge port by pulling and pushing the liquid in the droplet discharge port by using a predetermined actuator. In a droplet discharge apparatus that discharges a droplet by separating a droplet from a liquid column, a driving unit that applies a drive waveform for droplet discharge to the actuator for each droplet discharge; and the liquid A temperature variable element that is provided on an inner wall of a droplet discharge port and that changes the temperature of the liquid; and a temperature distribution setting unit that sets a temperature distribution in the liquid column using the temperature variable element, the temperature variable element Is supplied with an input signal corresponding to the droplet discharge driving waveform, and the temperature of the portion located near the inner wall of the droplet discharge port is set lower than the temperature of the constricted portion of the liquid column. Temperature distribution setting Providing a droplet discharge apparatus comprising the stage.

  According to the present invention, the temperature of the portion located near the inner wall of the droplet discharge port is set lower than the temperature of the constricted portion of the liquid column protruding from the droplet discharge port, so the vicinity of the inner wall of the droplet discharge port The conventional phenomenon that the liquid flows from the portion to the constricted portion no longer occurs. Therefore, the formation of the constricted shape (concave shape) of the constricted portion is accelerated, and the separation of the liquid droplet from the liquid column is facilitated.

  According to a second aspect of the present invention, in the first aspect of the present invention, the temperature variable element is a heating element that heats the liquid, and the temperature distribution setting unit is configured to discharge the droplet each time. There is provided a droplet discharge device characterized in that heating by the heating element is stopped after the heating element starts heating and after the driving waveform starts, but before the driving waveform ends.

  According to the present invention, the use of a heating element such as an electric resistance as the temperature variable element, that is, the liquid droplet can be easily separated with a simple configuration.

  According to a third aspect of the present invention, in the first aspect of the present invention, the temperature variable element is a cooling element that cools the liquid, and the temperature distribution setting unit is configured to discharge the droplet every time. A droplet discharge device is provided in which cooling by the cooling element is started after the start of the drive waveform and before the end of the drive waveform.

  According to the present invention, by actively cooling using the cooling element, the temperature of the portion of the liquid column located near the inner wall of the droplet discharge port can be directly cooled, so that the separation of the droplet is easier. become.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the temperature variable element is a heating / cooling element that heats and cools the liquid, and the temperature distribution setting means is a unit that discharges the liquid droplets. A droplet discharge device characterized by starting cooling by the heating / cooling element after the heating by the heating / cooling element and after the start of the driving waveform and before the end of the driving waveform each time I will provide a.

  According to the present invention, by heating and cooling using the heating / cooling element, the average temperature of the liquid in the droplet discharge port is not greatly increased or decreased even when droplets are continuously discharged. Therefore, the viscosity of the liquid in the droplet discharge port is stabilized, and the droplet discharge is stabilized.

  According to the present invention, when ejecting droplets by pulling control, the droplets can be easily separated from the liquid column.

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

  FIG. 1A is a perspective plan view showing an example of the overall structure of a droplet discharge head 50 according to the present invention.

  In FIG. 1A, a droplet discharge head 50 is a so-called full-line head, and is in a direction (arrow in the figure) perpendicular to the conveyance direction of the recording medium 16 (sub-scanning direction indicated by arrow S in the figure). In the main scanning direction indicated by M), a number of nozzles 51 (droplet discharge ports) that discharge liquid toward the recording medium 16 are two-dimensionally extended over a length (maximum recording width) corresponding to the width Wm of the recording medium 16. It has a structure that is arranged in order.

  In the droplet discharge head 50, a plurality of pressure chamber units 54 including a nozzle 51, a pressure chamber 52 communicating with the nozzle 51, and a liquid supply port 53 are predetermined in the main scanning direction M and the main scanning direction M. Are arranged along two oblique directions forming an acute angle θ (0 ° <θ <90 °). In FIG. 1A, only a part of the pressure chamber units 54 is illustrated for convenience of illustration.

  Specifically, the nozzles 51 are arranged at a constant pitch d in an oblique direction that forms a predetermined acute angle θ with respect to the main scanning direction M, and thus, “on a straight line along the main scanning direction M” d × cos θ ”can be handled equivalently.

  FIG. 1B shows a cross-sectional view along the line 1B-1B in FIG. 1A of the above-described pressure chamber unit 54 as one discharge element constituting the droplet discharge head 50. FIG.

  As shown in FIG. 1B, each pressure chamber 52 communicates with a common liquid chamber 55 via a liquid supply port 53. The common liquid chamber 55 communicates with a tank that is a liquid supply source (not shown), and the liquid supplied from the tank is distributed and supplied to each pressure chamber 52 via the common liquid chamber 55.

  A piezoelectric body 58a is disposed on the diaphragm 56 constituting the top surface of the pressure chamber 52, and an individual electrode 57 is disposed on the piezoelectric body 58a. The diaphragm 56 is grounded and functions as a common electrode. These diaphragm 56, individual electrode 57 and piezoelectric body 58a constitute a piezoelectric actuator 58 as means for generating a droplet discharge force.

  When a predetermined drive voltage is applied to the individual electrode 57 of the piezoelectric actuator 58, the piezoelectric body 58a is deformed to change the volume of the pressure chamber 52, and the pressure in the pressure chamber 52 is changed accordingly. A droplet is ejected. Specifically, by using the piezoelectric actuator 58 to pull (pull) and push (push) the liquid in the nozzle 51, the liquid column protrudes from the nozzle 51 and the liquid droplet is separated from the liquid column. Then, droplet discharge is performed. When the volume of the pressure chamber 52 returns to the original state after droplet discharge, new liquid is supplied from the common liquid chamber 55 through the liquid supply port 53 to the pressure chamber 52.

  A temperature variable element 31 is provided on the inner wall of the nozzle 51 to change the temperature of the liquid supplied from the pressure chamber 52 to the nozzle 51. By using this temperature variable element 31 to change the temperature of the liquid near the inner wall of the nozzle 51, the temperature distribution in the liquid column protruding from the nozzle 51 is set. The setting of the temperature distribution in the liquid column using the temperature variable element 31 will be described in detail later.

  There are various types of temperature variable elements 31. When a heating element that heats the liquid is used as the temperature variable element 31, the temperature variable element 31 can be easily configured, for example, by electric resistance. When a cooling element that cools the liquid is used as the temperature variable element 31, the liquid located near the inner wall of the nozzle 41 can be directly cooled. When a heating / cooling element that heats and cools the liquid is used as the temperature variable element 31, even when droplets are continuously discharged, the average temperature of the liquid in the nozzle 51 is not significantly increased or decreased. You can As the cooling element and the heating / cooling element, for example, a Peltier element having an effect (Peltier effect) that heat is transferred from one metal to the other metal when a current is passed through a joint between two kinds of metals. In the case of a heating / cooling element, a Peltier element that can switch the direction of movement of heat by reversing the current direction is used.

  The nozzle plate 21 on which the nozzles 51 are formed is fixed to the substrate 20 on which the pressure chambers 52 and the like are formed via the insulating layer 23. In other words, a heat insulating layer that also serves as an insulating layer is formed between the nozzle 21 and the substrate 20.

  The nozzle plate 21 is made of metal, and heat is radiated through the nozzle plate 20. A concave portion such as a groove or a convex portion may be formed on the surface (nozzle surface) 50a of the nozzle plate 21 to promote heat dissipation.

  FIG. 1A shows an example in which a plurality of nozzles 51 are two-dimensionally arranged as a structure capable of forming a high-resolution image on the recording medium 16 at a high speed. The droplet discharge head is not particularly limited to a structure in which a plurality of nozzles 51 are two-dimensionally arranged, and may have a structure in which a plurality of nozzles 51 are one-dimensionally arranged. Further, the pressure chamber unit 54 shown in FIG. 1B as an ejection element constituting the droplet ejection head is an example, and is not particularly limited to such a case. For example, instead of disposing the common liquid chamber 55 below the pressure chamber 52 (that is, the discharge surface 50a side than the pressure chamber 52), the common liquid is disposed above the pressure chamber 52 (that is, opposite to the discharge surface 50a). The chamber 55 may be disposed. Further, for example, instead of using the piezoelectric body 58a, a heating element may be used to generate the droplet discharge force.

  FIG. 2 is a block diagram showing an outline of the overall configuration of an example of the image forming apparatus 100 including the droplet discharge head 50 according to the present invention.

  In FIG. 2, the image forming apparatus 100 mainly includes a droplet discharge unit 12, a communication interface 110, a system controller 112, memories 114 and 152, a transport unit 116, a transport drive unit 118, a liquid supply unit 122, and a liquid supply drive unit 124. , A print control unit 150, a discharge drive unit 154, a temperature measurement unit 156, and a temperature distribution setting unit 158.

  In this example, liquid is ejected by four droplet ejection heads 50 (50K, 50C, 50M, 50Y) that eject inks of K (black), C (cyan), M (magenta), and Y (yellow), respectively. A droplet discharge unit 12 is configured.

  The communication interface 110 is an image data input unit that receives image data transmitted from the host computer 300. A wired or wireless interface can be applied to the communication interface 110. The image data taken into the image forming apparatus 100 by the communication interface 110 is temporarily stored in the first memory 114 for storing image data.

  The system controller 112 includes a microcomputer and its peripheral circuits, and is a main control unit that controls the entire image forming apparatus 100 according to a predetermined program. That is, the system controller 112 controls each unit such as the communication interface 110, the conveyance driving unit 118, the print control unit 150, and the like.

  The conveyance unit 116 is configured by rollers, a belt, and the like for conveying a recording medium such as paper. The transport unit 116 relatively moves the droplet discharge head 50 and the recording medium.

  The conveyance drive unit 118 is configured by a motor that drives the conveyance unit 116 in accordance with an instruction from the system controller 112 and its drive circuit.

  The liquid supply unit 122 includes an ink tank and a conduit as ink storage means for storing ink. Ink is supplied to the droplet discharge head 50 by the liquid supply unit 122.

  The liquid supply driving unit 124 includes a pump that drives the liquid supply unit 122 so that ink is supplied to the droplet discharge head 50 and a driving circuit thereof.

  The print control unit 150 includes a microcomputer and its peripheral circuits, and controls the liquid supply drive unit 124, the discharge drive unit 154, the temperature distribution setting unit 158, and the like according to a predetermined program.

  Based on the image data input to the image forming apparatus 100, the print control unit 150 forms droplets on the recording medium by causing each droplet discharging head 50 to discharge droplets (droplet ejection) toward the recording medium. The dot data necessary for this is generated. That is, the print control unit 150 performs image processing such as various processes and corrections for generating droplet ejection dot data from the image data in the first memory 114 according to the control of the system controller 112. The generated dot data is supplied to the ejection drive unit 154.

  The print controller 150 is accompanied by a second memory 152, and dot data and the like are temporarily stored in the second memory 152 during image processing in the print controller 150.

  In FIG. 2, the second memory 152 is shown as being attached to the print control unit 150, but it can also be used as the first memory 114. Also possible is an aspect in which the print controller 150 and the system controller 112 are integrated and configured with one processor.

  The ejection driving unit 154 is a ejection driving signal for each droplet ejection head 50 based on the dot data given from the print control unit 150 (actually, the dot data is stored in the second memory 152). Is output. In detail, the ejection driving unit 154 is independent of each of the plurality of piezoelectric actuators (58 in FIG. 1B) in the droplet ejection head 50 for each droplet ejection from the nozzle 51. A drive waveform for droplet ejection is given.

  The temperature measurement unit 156 is a known temperature measurement unit such as a thermometer that measures the temperature of ink supplied to the droplet discharge head 50. Instead of measuring the temperature of the ink, the temperature of the atmosphere may be measured.

  The temperature distribution setting unit 158 drives the temperature variable element 31 via a predetermined signal line, and sets the temperature distribution in the liquid column protruding from the nozzle 51 of the droplet discharge head 50. Specifically, each time a droplet is discharged from the nozzle 51 of the droplet discharge head 50, a droplet discharge drive waveform is given from the discharge drive unit 154 to the piezoelectric actuator 58 of the droplet discharge head 50. At this time, an input signal corresponding to the drive waveform for droplet discharge is applied to the temperature variable element 31 of the droplet discharge head 50 so that it is positioned closer to the inner wall of the nozzle 51 than the temperature of the constricted portion in the liquid column. Set the temperature of the portion (near the inner wall of the nozzle) low. The details of the temperature distribution setting will be described later in detail for each type of temperature variable element 31.

  Note that when the temperature distribution setting unit 158 sets the temperature distribution of the liquid column, it is preferable to change the input signal applied to the temperature variable element 51 based on the temperature measured by the temperature measurement unit 156. Specifically, the length of the heating time and / or the cooling time is changed based on the temperature of the ink (or the atmosphere) measured by the temperature measuring unit 156.

  The plurality of piezoelectric actuators 58 of the droplet discharge head 50 are individually driven by the discharge drive unit 154, while the plurality of temperature variable elements 31 of the droplet discharge head 50 are connected to the plurality of nozzles 51 by the temperature distribution setting unit 158. Are controlled in common. Thereby, the wiring structure between the temperature distribution setting unit 158 and the temperature variable element 31 of the droplet discharge head 50 can be simplified. On the other hand, the temperature variable element 31 of the droplet discharge head 50 may be individually controlled for each nozzle 51 by the temperature distribution setting unit 158.

  Hereinafter, the first embodiment using the heating element as the temperature variable element 31, the second embodiment using the cooling element as the temperature variable element 31, and the third embodiment using the heating and cooling element as the temperature variable element 31. The main configuration and temperature distribution setting process in each embodiment will be described separately.

[First Embodiment]
In the first embodiment, the temperature variable element 31 is configured by a heating element (also referred to as “heater”) having a predetermined electric resistance.

  FIG. 3A is an enlarged perspective plan view showing the nozzle 51 of the droplet discharge head 50 provided with the heater 31H as the temperature variable element 31 and its peripheral portion in an enlarged manner. 3B is a cross-sectional view taken along line 3B-3B in FIG. 3A, and FIG. 3C is a cross-sectional view taken along line 3C-3C in FIG.

  An annular heater 31H is provided on the inner wall of the nozzle 51 and in the vicinity of the nozzle surface 50a.

  The heater 31H is connected to the signal line 32. The resistance of the heater 31 </ b> H arranged around the nozzle 51 is higher than the resistance of the signal line 32. When the heater 31H is heated, the temperature of the liquid near the heater 31H, that is, the temperature of the liquid located near the inner wall of the nozzle 51 increases.

  Two insulating layers 23 </ b> I and 23 </ b> R are formed between the nozzle plate 21 and the substrate 20. The insulating layer 23R on the nozzle plate 21 side is thinner than the insulating layer 23I on the substrate 20 side. While the heat generated by the heater 30H is radiated from the nozzle plate 21 through the insulating layer 23R on the nozzle plate 21 side, the insulating layer 23I on the substrate 20 side has insulating properties and heat insulating properties.

  4 shows a drive signal 211 (actuator drive signal) given to the piezoelectric actuator 58 of the droplet discharge head 50 from the discharge drive unit 154 of FIG. 2, and a liquid velocity 212 (in the nozzle 51 of the droplet discharge head 50). Liquid velocity in the nozzle) and the input signal 213 (heater input signal) given to the heater 31H as the temperature variable element of the droplet discharge head 50 from the temperature distribution setting unit 158 in FIG. It is a timing chart which shows a correspondence.

  In FIG. 4, the actuator drive signal 211 is shown as a relative voltage with the initial voltage at which the piezoelectric actuator 58 is not displaced being “0” and the pull-side voltage being negative. Further, the liquid velocity 212 in the nozzle is set to “0” as an initial velocity at which no liquid moves with respect to the nozzle 51, the liquid movement to the push side is positive, and the liquid movement to the pull side is negative. Shown in relative speed. The input signal 213 of the heater is indicated by a relative current where the initial current without heating is “0” and the heating current is positive.

  In the actuator drive signal 211 shown in FIG. 4, a first pull drive signal 71, a first push drive signal 72, a second pull drive signal 73, and a second push drive signal 74 are continuously generated. A set of drive waveforms 70 is applied to the piezoelectric actuator 58, whereby one droplet (main droplet) is ejected from the nozzle 51.

  Specifically, as shown in FIG. 5A, the meniscus 79 in the nozzle 51 is temporarily retracted by the first pull drive signal 71. Subsequently, the liquid in the nozzle 51 is given a speed in the ejection direction (direction of arrow E in the figure) by the first push drive signal 72, and then the second pull drive signal 73 in the nozzle 51 Reduce the speed of the liquid. Then, after the liquid column 80 protrudes from the nozzle 51 as illustrated in FIG. 5C through the state illustrated in FIG. 5B, the main liquid droplet is separated from the liquid column 80.

  When one set of driving waveform 70 is given to the piezoelectric actuator 58 for each discharge of the main droplet, the liquid velocity 212 in the nozzle changes as shown in FIG.

  The concave shape (constriction shape) of the constricted portion 82 of the liquid column 80 shown in FIG. 5C is formed from the time t2 when the second pull drive signal 73 is given to the end time t3 of the drive waveform 70. The That is, it is formed between the time when the liquid velocity 212 in the nozzle reaches the maximum point and the velocity reaches “0”.

  In the temperature distribution setting process of the liquid column 80 in the present embodiment, heating by the heater 31H is performed at the time t0 (or a predetermined time before t0) of the first pull drive signal 71 for each discharge of one main droplet. The heating by the heater 31H is stopped between the application time t1 of the first push drive signal 72 and the end time t3 of the drive waveform 70 at the latest.

  Actually, as shown in FIG. 5 (A), from the state in which the meniscus 79 in the nozzle 51 is most retracted, until the liquid column 80 grows and the liquid velocity 212 in the nozzle becomes “0” ( That is, heating by the heater 31H is stopped until no new liquid is supplied to the liquid column 80 until the volume of the liquid column 80 becomes the largest.

  The heater input signal 213 shown in FIG. 4 starts heating by the heater 31H in synchronization with the first pull signal 71 and stops heating by the heater 31H in synchronization with the first push drive signal 72. This is indicated by a solid line. As described above, the heating by the heater 31H can be easily stopped in synchronization with the first push drive signal 72 or stopped in synchronization with the second pull signal 73. In some cases, the second push signal 74 may be synchronized.

  In short, as shown in FIG. 5C, before the constricted shape of the constricted portion 82 appears before the volume of the liquid column 80 becomes the largest, the heating by the heater 31H and the nozzle plate 51 are stopped. Due to the heat radiation, the temperature of the portion near the nozzle 81 of the liquid column 80 is set lower than the temperature of the constricted portion 82.

  More preferably, the change in the liquid velocity 212 in the nozzle is obtained by simulation or experiment, and the heating stop timing is determined. Preferably, the heating by the heater 31H is stopped between the time when the liquid velocity 212 in the nozzle switches from negative to positive (corresponding to t1) and the time when the liquid velocity 212 in the nozzle reaches the maximum (corresponding to t2).

[Second Embodiment]
In the second embodiment, the temperature variable element 31 is configured by a Peltier element.

  6A is an enlarged perspective view showing the nozzle 51 of the droplet discharge head 50 provided with the Peltier element 31P as the temperature variable element 31 and its peripheral portion in an enlarged manner. 6B shows a cross-sectional view taken along line 6B-6B in FIG. 6A, and FIG. 6C shows a cross-sectional view taken along line 6C-6C in FIG. 6A.

  An annular Peltier element 31P is provided on the inner wall of the nozzle 51 and in the vicinity of the nozzle surface 50a.

  The Peltier element 31P has two electrodes 31a and 31b. These electrodes 31a and 31b are connected to different signal lines 32a and 32b, respectively.

  Two insulating layers 23 </ b> I and 23 </ b> R are formed between the nozzle plate 21 and the substrate 20. The insulating layer 23R on the nozzle plate 21 side is thinner than the insulating layer 23I on the substrate 20 side. The heat of the Peltier element 31P is conducted from the nozzle plate 21 to the outside air through the insulating layer 23R on the nozzle plate 21 side, while the insulating layer 23I on the substrate 20 side has insulating properties and heat insulating properties.

  7 shows a drive signal 211 (actuator drive signal) given from the ejection drive unit 154 of FIG. 2 to the piezoelectric actuator 58 of the droplet ejection head 50, and a liquid velocity 212 (in the nozzle 51 of the droplet ejection head 50). Liquid velocity in the nozzle) and an input signal 214 (input signal of the Peltier element) given from the temperature distribution setting unit 158 of FIG. 2 to the Peltier element 31P as the temperature variable element of the droplet discharge head 50 It is a timing chart which shows the correspondence of a series.

  In FIG. 7, the actuator drive signal 211 and the liquid velocity 212 in the nozzle are the same as those in the first embodiment shown in FIG. The input signal 214 of the Peltier element in the present embodiment is indicated by a relative current where the initial current without cooling is “0” and the cooling current is negative.

  In the temperature distribution setting process of the liquid column 80 in the present embodiment, the cooling by the Peltier element 31P is not performed at the application time point t0 of the first pull drive signal 71 every time one main droplet is ejected. The cooling by the Peltier element 31P is started between the application time t1 of the push drive signal 72 and the end time t3 of the drive waveform 70 at the latest.

  Actually, as shown in FIG. 5 (A), from the state in which the meniscus 79 in the nozzle 51 is most retracted, until the liquid column 80 grows and the liquid velocity 212 in the nozzle becomes “0” ( That is, the cooling by the Peltier element 31P is started until there is no new liquid supply to the liquid column 80 and the volume of the liquid column 80 becomes the largest.

  The Peltier element input signal 214 shown in FIG. 7 is indicated by a solid line when cooling by the Peltier element 31P is started in synchronization with the first push drive signal 72. Thus, the cooling by the Peltier element 31P can be easily started in synchronization with the first push drive signal 72 or can be started in synchronization with the second pull signal 73. In some cases, the second push signal 74 may be synchronized.

  In short, as shown in FIG. 5C, before the constricted shape of the constricted portion 82 appears before the volume of the liquid column 80 becomes the largest, cooling by the Peltier element 31P and heat radiation by the nozzle plate 51 are performed. Thus, the temperature in the vicinity of the nozzle 81 of the liquid column 80 is set lower than the temperature in the constricted portion 82.

  More preferably, the change of the liquid velocity 212 in the nozzle is obtained by simulation or experiment, and the cooling start timing is determined. Preferably, the cooling by the Peltier element 31P is started from the time (corresponding to t1) when the liquid velocity 212 in the nozzle switches from negative to positive (corresponding to t1) to the time (corresponding to t2) when the liquid velocity 212 in the nozzle becomes maximum. .

  Further, the cooling by the Peltier element 31P stops until the next main droplet discharge control is started, that is, at the latest by the start time t0 of the next drive waveform 70.

[Third Embodiment]
In the third embodiment, the temperature variable element 31 is configured by a Peltier element that performs heating and cooling.

  8 shows a drive signal 211 (actuator drive signal) given to the piezoelectric actuator 58 of the droplet discharge head 50 from the discharge drive unit 154 of FIG. 2, and a liquid velocity 212 (in the nozzle 51 of the droplet discharge head 50). Liquid velocity in the nozzle) and an input signal 215 (input signal of the Peltier element) given from the temperature distribution setting unit 158 of FIG. 2 to the Peltier element 31P as the temperature variable element of the droplet discharge head 50 It is a timing chart which shows the correspondence of a series.

  In FIG. 8, the actuator drive signal 211 and the liquid velocity 212 in the nozzle in this embodiment are the same as those in the first embodiment shown in FIG. The input signal 215 of the Peltier element in the present embodiment is represented by a relative current where the initial current without heating and cooling is “0”, the heating current is positive, and the cooling current is negative.

  In the temperature distribution setting process of the liquid column 80 in the present embodiment, heating by the Peltier element 31P is performed at the time t0 (or a predetermined time before t0) when the first pull drive signal 71 is applied for each discharge of one main droplet. The heating is stopped and the cooling is started by the Peltier element 31P between the application time t1 of the first push drive signal 72 and the end time t3 of the drive waveform 70 at the latest.

  Actually, as shown in FIG. 5 (A), from the state in which the meniscus 79 in the nozzle 51 is most retracted, until the liquid column 80 grows and the liquid velocity 212 in the nozzle becomes “0” ( That is, until no new liquid is supplied to the liquid column 80 and the volume of the liquid column 80 is maximized), the Peltier element 31P stops heating and starts cooling.

  The Peltier element input signal 215 shown in FIG. 8 starts to be heated by the Peltier element 31P in synchronization with the first pull signal 71 and is also heated by the Peltier element 31P in synchronization with the first push drive signal 72. The case where the stop and the cooling start are performed is indicated by a solid line. In this way, it is easy to stop heating and start cooling by the Peltier element 31P in synchronization with the first push drive signal 72 or in synchronization with the second pull signal 73. In some cases, the second push signal 74 may be synchronized.

  In short, as shown in FIG. 5C, before the constricted shape of the constricted portion 82 appears before the volume of the liquid column 80 becomes the largest, the heating is stopped and the cooling is started by the Peltier element 31P and the nozzle. Due to heat radiation by the plate 51, the temperature of the nozzle vicinity portion 81 of the liquid column 80 is set lower than the temperature of the constricted portion 82.

  More preferably, the change in the liquid velocity 212 in the nozzle is obtained by simulation or experiment, and the timing of stopping heating and starting cooling is determined. Preferably, the cooling by the Peltier element 31P is started from the time (corresponding to t1) when the liquid velocity 212 in the nozzle switches from negative to positive (corresponding to t1) to the time (corresponding to t2) when the liquid velocity 212 in the nozzle becomes maximum. .

  Further, the cooling by the Peltier element 31P is stopped until the next main droplet discharge control is started, that is, by the start point t0 of the next drive waveform at the latest.

  In any of the first to third embodiments, as shown in FIG. 5C, a portion located near the inner wall of the nozzle 51 than the temperature of the constricted portion 82 of the liquid column 80 protruding from the nozzle 51. Since the temperature of 81 (near the nozzle inner wall) is set low, the conventional phenomenon that the liquid flows from the nozzle inner wall vicinity 81 to the constricted portion 82 does not occur, but also from the constricted portion 82 to the nozzle inner wall proximate portion 81. Liquid flow 821 is generated. Therefore, the formation of the constricted shape (concave shape) of the constricted portion 82 becomes faster, and the main droplet from the liquid column 80 can be easily divided.

  As mentioned above, although embodiment of this invention was described in detail, this invention is not limited to the example demonstrated in this specification and the example shown in drawing, In the range which does not deviate from the summary of this invention, various Design changes and improvements may be made.

(A) is a plane perspective view showing the overall structure of the droplet discharge head, and (b) is a cross-sectional view taken along the line bb. 1 is a block diagram illustrating an overall configuration of an image forming apparatus. FIG. 2 is an enlarged view showing an enlarged periphery of a nozzle when a heating element is provided in the liquid discharge head of FIG. It is explanatory drawing used for description of the temperature setting of the liquid column using a heating element. It is a schematic diagram which shows the mode of the change of the meniscus by the drive of an actuator. FIG. 2 is an enlarged view showing an enlarged periphery of a nozzle when a Peltier element is provided in the liquid ejection head of FIG. It is explanatory drawing used for description of the temperature setting of the liquid column which used the Peltier device as a cooling element. It is explanatory drawing used for description of the temperature setting of the liquid column which used the Peltier device as a heating-cooling element. It is explanatory drawing used for description of the temperature distribution in a liquid column at the time of applying the conventional droplet separation technique to the droplet apparatus which discharges a droplet by pulling.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 21 ... Nozzle plate, 31 ... Temperature variable element (heater, Peltier element), 32 ... Electrode layer, 50 ... Droplet discharge head, 50a ... Nozzle surface, 51 ... Nozzle (droplet discharge port), 52 ... Pressure chamber, 58 ... Piezoelectric actuator, 70 ... Drive waveform, 71 ... First pull signal, 72 ... First push signal, 73 ... Second pull signal, 74 ... Second push signal, 150 ... Print controller, 154 ... Discharge Driving unit, 156 ... temperature measuring unit, 158 ... temperature distribution setting unit, 213 ... input signal of heater as heating element, 214 ... input signal of Peltier element as cooling element, 215 ... input of Peltier element as heating / cooling element signal

Claims (4)

A liquid droplet is ejected by pulling and pushing the liquid in the liquid droplet ejection port using a predetermined actuator to cause the liquid column to protrude from the liquid droplet ejection port and to separate the liquid droplet from the liquid column. In the discharge device,
Driving means for providing a driving waveform for droplet ejection to the actuator for each droplet ejection;
A temperature variable element that is provided on the inner wall of the droplet discharge port and that changes the temperature of the liquid;
A temperature distribution setting means for setting a temperature distribution in the liquid column using the temperature variable element, giving an input signal corresponding to the droplet discharge drive waveform to the temperature variable element; Temperature distribution setting means for setting a temperature of a portion located near the inner wall of the droplet discharge port to be lower than a temperature of a constricted portion of the liquid column;
A droplet discharge apparatus comprising: The temperature variable element is a heating element for heating the liquid,
The temperature distribution setting means performs heating by the heating element after the start of heating by the heating element and after the start of the driving waveform and before the end of the driving waveform for each droplet discharge. The droplet discharge device according to claim 1, wherein the droplet discharge device is stopped. The temperature variable element is a cooling element that cools the liquid,
The temperature distribution setting means starts cooling by the cooling element after the start of the drive waveform and before the end of the drive waveform for each droplet discharge. 2. The droplet discharge device according to 1. The temperature variable element is a heating / cooling element for heating and cooling the liquid,
The temperature distribution setting means uses the heating / cooling element after the start of heating by the heating / cooling element and after the start of the driving waveform and before the end of the driving waveform for each droplet discharge. The droplet discharge device according to claim 1, wherein cooling is started.

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