JP2009106873A - Method for controlling discharge of liquid drop and apparatus for discharging liquid drop - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling discharge of liquid drops and an apparatus for discharging liquid drops which continuously discharge liquid drops in a uniform amount at a constant speed from the first liquid drop. <P>SOLUTION: The apparatus for discharging liquid drops includes an inkjet head 1 discharging a liquid agent 11, a liquid agent tank 2 connected to the inkjet head 1, a pressure controlling part 3 controlling pressure to the liquid agent tank 2, an image pick-up part 7 and an image processing part 9 imaging the top end of the nozzle head 1 and processing the image, and a controller 10 controlling discharge conditions, image processing and pressure. A meniscus 12 at the time of non-discharge is made to be an expanded convex shape at the top end of the nozzle head 1 by controlling the pressure applied to the liquid agent tank 2, a distance and an angle between the top end of the nozzle head 1 and the top end od the meniscus 12 are measured by imaging-image processing through the image pick-up part 7 and the image processing part 9, and the meniscus 12 is controlled to a predetermined convex meniscus 12 by comparing with a preliminarily memorized optical meniscus 12 and a meniscus 12 at the time of auxiliary discharge. Thus stable discharge conditions can be obtained from the first liquid drop. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a droplet discharge control method and a droplet discharge apparatus for discharging a liquid agent using an inkjet head. More specifically, the present invention relates to a technique for stably discharging droplets by controlling a meniscus amount in an inkjet head.

  When discharging a liquid agent by an inkjet method, as an important element for stably discharging a liquid agent, a meniscus in an inkjet head that discharges the liquid agent (a surface where the liquid agent in the nozzle comes into contact with the atmosphere: more specifically, the liquid agent in the nozzle There is a control of the curved liquid surface that occurs due to the magnitude relationship between the adhesion force acting between them and the cohesive force between liquid molecules when in contact with the atmosphere. As a control method, an optical waveguide is disposed so as to be in contact with the passage of the liquid agent in the inkjet head, a laser beam is input to the optical waveguide, and a change in the amount of light due to the presence or absence of the liquid agent in the optical waveguide portion is measured. Thus, a method for controlling the meniscus (see, for example, Patent Document 1) and a method for realizing a prescribed meniscus by attaching a pressure sensor to a liquid agent tank connected to a nozzle and controlling the pressure based on the value of the sensor ( For example, refer to Patent Document 2) and a method of controlling the meniscus by changing the water head difference between the liquid agent tank, the liquid agent tank, and the head for the purpose of changing the amount of liquid to be discharged (see, for example, Patent Document 3).

  In addition, there is a method for controlling the meniscus by controlling the voltage applied to the piezoelectric ceramic for the same purpose (for example, see Patent Document 4), and further, the purpose of preventing the liquid agent from drying and improving the ejection stability. Thus, there is a method of vibrating the meniscus by controlling the voltage applied to the piezoelectric ceramics to such an extent that the ink jet head does not discharge during non-ejection (see, for example, Patent Document 5).

The meniscus shape in these cases is not particularly described with respect to Patent Document 1, but in other Patent Documents 2 to 5, for example, as shown in FIGS. 11 and 12, a shear mode type ink jet method using piezoelectric ceramics. The meniscus 12 of the medicine 11 is not on the discharge side but in the minus direction in the head axis direction from the tip of the inkjet head 1 in all cases (that is, the liquid from the inkjet head has a concave shape). The control method is always used.
JP 2005-178290 A JP 200445070 A JP-A-5-169678 JP 2000-218817 A JP 2004-202740 A

  In recent years, there has been a growing need to use inkjet droplet ejection devices not only for printers but also for manufacturing processes that require the application and ejection of a small amount of liquid agent. There is a growing demand for the accuracy of landing and the amount of liquid. Under such circumstances, when the first droplet, which is the first droplet, is ejected, the state shifts from a stable state, which is a non-ejection state, to another state / operation, which is ejection of a liquid agent. Therefore, even in processes that require stable application and discharge to the target object, the liquid material scatters to unnecessary parts due to satellites, defects due to differences in application and discharge amounts, and landing positions due to unstable discharge directions There is concern about the occurrence of abnormalities. In other words, in order to always obtain a stable discharge state, it is necessary to stabilize the discharge state of the first droplet, which is the first droplet that is most difficult to stabilize the discharge state. In the case of a process that becomes effective and requires a predetermined amount to be accurately discharged to a certain place, there is no satellite from the first drop, and a stable discharge amount is required.

  However, in the conventional meniscus control, the meniscus before ejection is slightly depressed inward in the minus direction with respect to the axial direction of the head, that is, at the tip of the ink jet head, so that the liquid agent does not leak when the ink jet head is moved. It is controlled to have a concave shape. Therefore, since the position and shape of the meniscus cannot be observed from the outside of the inkjet head, it cannot be accurately grasped, and even if the discharge is stable during continuous discharge, the same discharge state can be obtained from the first drop of discharge. was difficult.

  Furthermore, it is expected that the meniscus state at the tip of the inkjet head will change due to changes in the environment and characteristics of the liquid agent, as well as changes in pressure on the liquid agent due to changes in the remaining amount. In other words, as described as a problem in the past patent documents, the speed and amount of the liquid droplets change depending on the amount of the meniscus, and the position and shape of the meniscus cannot be accurately grasped. There is a problem that it is very difficult to stabilize the discharge state.

  The present invention solves the problems and problems of the conventional droplet discharge control method and droplet discharge device, and is capable of realizing stable discharge from the first droplet and a droplet discharge. An object is to provide an apparatus.

  In order to solve the above-described conventional problems, a droplet discharge control method according to the present invention is a droplet discharge control method for discharging a liquid agent from an inkjet head, and the liquid agent at the tip of the inkjet head before discharging the first droplet The meniscus is controlled to have a convex shape.

  In addition, the droplet discharge device of the present invention includes an inkjet head that discharges a liquid agent, a liquid agent tank that supplies the liquid agent to the inkjet head, a pressure control unit that controls a tank pressure to the liquid agent tank, and the inkjet head An image photographing unit that photographs the meniscus of the liquid agent at the tip and outputs an image signal thereof, and a pressure control unit command signal that controls the pressure control unit based on image information of the meniscus that bulges from the tip of the inkjet head And a control device for outputting.

  According to the droplet discharge control method and the droplet discharge device of the present invention, the first meniscus state before discharging the first droplet is made convex so that the first droplet is discharged and the case of continuous discharge The liquid agent can be discharged at the same discharge amount and discharge speed as in the above, and a stable discharge state can be realized from the first drop of discharge. That is, generally in the continuous discharge state, it is discharged in a state where the meniscus is convex at the tip of the inkjet head, and the liquid agent can be discharged at a stable discharge amount and discharge speed in the continuous discharge state. From the first droplet, the meniscus can be maintained in a state similar to the non-ejection state between the ejection timings in the continuous ejection state, and stable ejection can be achieved. In addition, since the meniscus before the first droplet is ejected has a convex shape, the meniscus can be visualized and controlled, so that the change in the liquid discharge state due to the environmental state of the liquid and the amount of liquid are reduced. Therefore, it is possible to cope with a change in pressure applied to the liquid agent acting on the liquid agent tank or the tip of the inkjet head. Furthermore, even when the liquid agent is a concern that may occur when the head is moved, the state of the tip of the inkjet head can be monitored and visualized at all times, so that a stable state can be maintained.

  In addition, as the meniscus of the liquid agent at the tip of the inkjet head before discharging the first droplet, the optimal meniscus state stored in advance and the bulging dimension of the meniscus state at the time of continuous discharge, or the bulging angle of a specific location, Alternatively, the optimum meniscus state can always be maintained by controlling the pressure applied to the liquid agent tank so as to approach the bulge area, the bulge angle, and the bulge area as compared with the bulge area.

Hereinafter, a droplet discharge control method and a droplet discharge apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.
First, a schematic configuration of the droplet discharge device of the present invention will be described. FIG. 1 is an overall perspective view of a droplet discharge device according to an embodiment of the present invention, and FIG. 2 is a diagram schematically showing a main part of the droplet discharge device from the side.

  As shown in FIG. 1 and FIG. 2, the droplet discharge device according to the embodiment of the present invention applies a liquid agent (liquid) to a target medium 5 as a discharge target (except in the case of preliminary discharge described later). An ink jet head 1 for discharging droplets 4), a liquid agent tank 2 for supplying a liquid agent to the ink jet head 1, a pressure control unit 3 for controlling a tank pressure to the liquid agent tank 2, an ink jet head 1 and a liquid agent tank 2 A head holder 6 to be held, an image capturing unit 7 as an image capturing unit that captures an image of the meniscus 12 (see FIGS. 3 to 7) at the tip of the inkjet head 1 and outputs an image signal thereof. And a control device for outputting a pressure control unit command signal for controlling the pressure control unit 3 based on the image information of the captured meniscus 12 and the image processing unit 9 for processing the captured image It has a such as 0. Then, the shape of the meniscus 12 at the tip of the inkjet head 1 (hereinafter also referred to as the tip of the inkjet head 1) is imaged by the imaging unit 7, and the pressure control unit 3 is controlled based on the image information of the captured meniscus 12. By being controlled by 10, the meniscus 12 of the liquid 11 at the tip of the inkjet head 1 can be adjusted to a predetermined shape.

  Next, the gist of the droplet discharge control method according to the embodiment of the present invention will be described. FIGS. 3A and 3B are cross-sectional views showing the state of the meniscus at the tip of the inkjet head during non-ejection in this droplet ejection control method, and simultaneously show the dimensions important for meniscus formation described later. Yes.

  Here, an object of the present invention is to control the meniscus 12 formed at the tip of the inkjet head 1 to an optimal shape, and a stable ejection state from the first droplet, which is the first droplet during ejection, that is, continuous. It is to obtain a discharge state with the same liquid amount and droplet speed as the state immediately before the discharge of each droplet at the time of discharge.

  As shown in FIGS. 3A and 3B, the droplet discharge control method according to the embodiment of the present invention is a non-discharge state before discharging at least the first droplet (hereinafter simply referred to as non-discharge). The shape of the meniscus 12 at the tip of the inkjet head 1 at the time of discharge) bulges from the tip of the inkjet head 1 with respect to the axial direction T of the inkjet head 1, and is a convex shape having a certain size range, which will be described later It is characterized by. In order to achieve the object, the shape of the meniscus 12 at the time of non-ejection and the shape of the meniscus 12 at the time of continuous ejection are set to the same state or close to each other. The shape of the meniscus 12 requires a state of slightly bulging from the tip of the ink jet head 1, and the optimum shape of the meniscus 12 regardless of whether the amount of the liquid 11 that forms the meniscus 12 is large or small. Therefore, the optimum discharge state cannot be obtained.

  First, the inkjet head 1 and the liquid agent 11 of this Embodiment are demonstrated. As the inkjet head 1, one having an inner diameter of about 50 μm and an outer diameter of about 550 μm was used. The liquid agent 11 is a solution using water as a solvent, and has a viscosity of 0.9 to 1.0 mPa · s at an atmospheric temperature of about 25 ° C.

  In the present embodiment, in order to obtain an optimal shape of the meniscus 12, the shape of the meniscus 12 at the tip of the inkjet head 1 (hereinafter also referred to as the shape of the meniscus 12) is imaged by the imaging unit 7, and the image processing unit 9 performs FIG. A distance (that is, a bulging dimension from the front end of the ink jet head 1) A from the front end of the ink jet head 1 to the front end M0 of the meniscus 12 during non-ejection shown in (a), an end surface of the ink jet head 1, and a front end M0 of the meniscus 12 An angle (bulging angle) θa formed by a straight line connecting the two, and an arbitrary distance C (about 190 μm in this embodiment) from the center (axial center T) of the inkjet head 1 as shown in FIG. ) From the intersection M1 (specific point) of the imaginary line T1 in the axial direction of the ink-jet head 1 and the meniscus 12 away from the ink-jet head. The distance (bulging dimension) B to the tip of the printing head 1 and an angle (bulging angle) θb formed by a straight line connecting the intersection M1 and the end face of the inkjet head 1 are measured as predetermined dimensions. In the liquid agent 11 made of a certain solution using water as a solvent in the present embodiment, the distance A: 15 to 20 μm, the angle θa: 3.2 to 4.4 °, and about 190 μm from the axis T of the inkjet head 1. The distance B at the intersection M1 with the meniscus 12 that is separated by a distance B: 7.5 μm to 13 μm and the angle θb: 5.4 to 9.2 ° are dimension values that can obtain the optimum meniscus 12. Instead of these dimension values, the area value (bulge area) of the meniscus 12 that forms a convex shape during non-ejection in the image processing may be within a predetermined range.

  FIG. 4 is a cross-sectional view showing the state of the meniscus 12 at the tip of the inkjet head 1 during continuous ejection, and simultaneously shows dimensions important for forming a predetermined shape of the meniscus 12. As described above, it is important that the shape of the meniscus 12 at the time of non-ejection and the shape of the meniscus 12 at the time of continuous ejection are close or the same. Here, the meniscus 12 at the center (axial center T) of the ink jet head 1 to which the droplets 4 are continuously ejected is slightly convex, but from the tip of the ink jet head 1 to the tip of the meniscus 12 formed. The distance (bulging dimension) A ′ is slightly shorter than the above-mentioned (bulging dimension) distance A, and is different from a predetermined dimension value in the meniscus 12 shape at the time of non-ejection. However, from the intersection M0 between the imaginary line T1 in the axial direction of the inkjet head 1 and the meniscus 12 which is separated from the center (axial center) of the inkjet head 1 by an arbitrary distance C (about 190 μm in the present embodiment), the inkjet head. The distance (bulging dimension) B to one tip and the angle θb formed by the straight line connecting the intersection and the end face of the inkjet head 1 are in the same state as the dimension formed by the meniscus 12 during non-ejection. Therefore, the distance B and the angle θb are used as the predetermined dimensions when comparing the meniscus 12 at the time of non-ejection and the meniscus 12 at the time of ejection. In other words, in the present embodiment, the distance B at the intersection M0 between the imaginary line T1 in the axial direction of the inkjet head 1 and the meniscus 12 that is about 190 μm away from the center (axial center T) of the inkjet head 1 is 7.5 μm. ˜13 μm and angle θb: 5.4 to 9.2 ° are dimension values that can obtain the optimum meniscus 12.

  On the other hand, when the meniscus 12 shape becomes a concave shape or an excessively convex shape in the present embodiment for achieving the object of the present invention, the liquid droplet 4 is discharged during continuous discharge in which the liquid droplet 4 is repeatedly discharged to some extent. Although the behavior and liquid volume are stabilized, it is difficult to stabilize the behavior and liquid volume of the droplet 4 from the first drop of discharge, and the speed and liquid volume of the satellite and the droplet 4 are changed, so that the same discharge state is obtained. It ’s difficult.

  Here, the behavior of the meniscus 12 at the time of non-ejection in the optimum state and the state at the time when it is not, and the behavior at the time of continuous ejection will be described. The discharge conditions, discharge signals, and imaging conditions sent from the control device 10 to the inkjet head 1 and the image processing unit 9 are the same for all images captured and processed by the imaging unit 7 and the image processing unit 9. Do.

  First, FIGS. 5A, 5B, and 5C show the optimum shape of the meniscus 12 at the time of non-ejection, the ejection state of the droplet 4 as the first droplet at that time, the meniscus 12 and the droplet at the time of continuous ejection. 4 shows the behavior. FIG. 5A shows a case where the non-ejection meniscus 12 shape is within an allowable range of a predetermined dimension (or the area value of the meniscus 12), and FIG. 5B shows that the ejection signal is output. The distance X from the front end of the inkjet head 1 of the first droplet 4 indicates the state when a predetermined time has elapsed from the start of the inkjet head 1 of FIG. 5 (c). The distance X is almost the same as the distance X. This is because the meniscus 12 at the time of non-ejection which can obtain a stable ejection state from the first ejection droplet is formed.

  On the other hand, for example, as shown in FIG. 6A, the amount of the liquid 11 that forms the meniscus 12 at the time of non-ejection is large, and the distance A from the front end of the inkjet head 1 to the front end of the meniscus 12 is a distance Y greater than a predetermined dimension. When it is long (the meniscus 12 has a large area value), as shown in FIG. 6B, the distance X1 of the first droplet 4 from the tip of the inkjet head 1 is as shown in FIG. The position of the droplet 4 during stable continuous ejection is a position that is closer to the inkjet head 1 by the distance Z. This is because the amount of liquid forming the meniscus 12 is increased, the amount of liquid of the first droplet 4 is increased, the speed of the droplet is decreased, and the discharge timing of the droplet 4 is stable. It is estimated that this is delayed compared to the continuous discharge. Therefore, as shown in FIG. 7A, the captured image of the discharged droplet 4 at a predetermined timing is obtained when the first droplet 4a is discharged after the first droplet 4a is discharged. The behavior of the droplet 4a gradually approaches the position / liquid amount of the droplet 4e during continuous ejection.

  For example, as shown in FIG. 8A, the amount of the liquid 11 that forms the meniscus 12 at the time of non-ejection is small, and the distance A from the front end of the ink jet head 1 to the front end of the meniscus 12 is shorter than a predetermined dimension. In the case where the tip end is close to a concave shape (the area value of the meniscus 12 is small), as shown in FIG. 8B, the distance X2 of the first droplet 4 from the tip end of the inkjet head 1 is as shown in FIG. The position of the droplet 4 at the time of stable continuous discharge as shown in (c) is a position away from the tip of the inkjet head 1 by a distance Z. This is because the liquid volume of the first droplet 4 is reduced by the amount of liquid of the meniscus 12 being reduced, so that the liquid droplet speed is increased and the discharge timing of the liquid droplet 4 is discharged stably. This is presumed to be faster than time. Therefore, as shown in FIG. 7B, the captured image of the discharged droplet 4 at a predetermined timing is obtained when the first droplet 4a is discharged after the first droplet 4a is discharged. The behavior of the droplet 4a gradually approaches the position / liquid amount of the droplet 4e during continuous ejection. Further, when the amount of liquid forming the meniscus 12 is extremely large or small, the droplet 4 is not ejected for a while, a satellite phenomenon in which the droplet 4 becomes plural, or the directionality of the droplet 4 occurs. Leads to phenomena such as instability.

  Further, as shown in the conventional example of FIG. 11 or FIG. 12, when the meniscus 12 is formed in a minus direction (concave shape) with respect to the axial direction of the inkjet head 1 (that is, formed so as to be depressed), the discharge is performed during continuous discharge. Since the state is stable, there is no problem, but the position and shape of the meniscus 12 cannot be accurately grasped, so it is difficult to obtain the same state (liquid amount / droplet speed) from the first drop of ejection.

  Further, when looking at the time axis, the shape of the meniscus 12 is caused by a change in characteristics such as viscosity due to an environmental change of the liquid 11 or a change in pressure acting on the meniscus 12 at the tip of the inkjet head 1 due to a change in the remaining amount of the liquid 11 in the liquid tank 2. Is expected to change over time. In that case, since the position and shape of the meniscus 12 cannot be accurately grasped, it becomes more difficult to make the discharge state the same as that during continuous discharge from the first drop.

  On the other hand, according to the present invention, the meniscus 12 at the time of non-ejection is controlled to an optimum meniscus 12 state that is a convex shape (a bulging shape) within an allowable range of a predetermined dimension (or area value). Thus, it is possible to obtain a stable ejection state from the first droplet which is the first droplet, that is, an ejection state equivalent to that during continuous ejection.

  Next, the droplet discharge apparatus according to the embodiment of the present invention will be described in more detail with reference to FIGS. 2 schematically shows a state in which the tip of the nozzle head 1 is imaged by the imaging unit 7 at a standby position (a standby position where no ejection is performed with respect to the ejection medium 5).

  As shown in FIG. 1, an inkjet head 1 that discharges a liquid agent 11 (see FIG. 3 and the like) is mounted on a nozzle head holder 6 that also holds a liquid agent tank 2, and discharge conditions set by a control device 10, The droplet 4 is ejected by the ejection signal. In this embodiment, the liquid agent tank 2 is disposed such that the bottom surface of the liquid agent tank 2 is higher than the tip of the inkjet head 1 in order to cope with a wide area of the target medium (target object to be ejected) 5.

  Further, as shown in FIG. 1, an imaging unit 7 is arranged at a standby position where the target medium 5 is not ejected so that the front end of the inkjet head 1 can be imaged, so that preliminary ejection can be performed. ing. Here, the preliminary ejection does not mean that the target medium 5 is ejected, but means that prior ejection confirmation is performed. And as above-mentioned, it has the image processing part 9 which processes the image imaged by the said imaging part 7, and the pressure control part 3 for supplying negative or positive pressure to the liquid agent tank 2, These images The processing unit 9 and the pressure control unit 3 are respectively connected to the control device 10 and configured to control the image processing unit 9 and the pressure control unit 3 by sending signals from the control device 10 in accordance with each processing. Note that the standby position for avoiding the target medium 5 is arranged so as not to come into contact with other devices or the like even if the inkjet head 1 or the imaging unit 7 moves. Further, when the tip of the inkjet head 1 is arranged lower than the liquid agent tank 2 as in the present embodiment, the liquid agent 11 often hangs from the tip of the inkjet head 1 due to a water head difference if nothing is done. At the time of non-ejection, a negative pressure is applied to the liquid agent tank 2.

  Here, the imaging unit 7 can image the inkjet head 1 at the standby position, and at the same time, always captures and grasps the shape of the meniscus 12 formed at the tip of the inkjet head 1 at the time of non-ejection. Further, not only during non-ejection, but also during preliminary ejection, the droplet 4 ejected from the inkjet head 1 can be imaged at an arbitrary timing from the signal from the control device 10 and image processing can be performed. For example, as shown in FIGS. 5A, 5 </ b> B, and 5 </ b> C, the tip of the inkjet head 1 and the meniscus 12 shape during non-ejection and ejection, and the droplet 4 to be ejected are imaged by the imaging unit 7 and image processing is performed. It can be processed and measured by the unit 9. Further, in order to control the shape of the meniscus 12 at the tip of the ink jet head 1 at the time of non-ejection to the convex meniscus 12 shape that can obtain the optimum ejection state as described above, the liquid agent that supplies the liquid agent 11 to the ink jet head 1. This is realized by controlling the pressure applied to the tank 2 by the pressure control unit 3.

  Next, a droplet discharge control method for controlling the meniscus 12 in the present embodiment will be described. FIG. 9 is an example showing a flow of control operation of the droplet discharge control method according to the present embodiment. First, the non-ejection meniscus 12 shape is imaged by the imaging unit 7 at the standby position (step S1). Then, the image processing unit 9 measures the predetermined dimension (or angle or area value) of the captured image (step S2), and the preliminarily stored optimal (set) dimension (or specified angle or area) of the meniscus 12 is stored. It is compared with (specified area value) (step S3). If the compared value is within the allowable range, the process proceeds to the step of discharging to the target medium 5 (steps S6 and S7). However, if it is outside the permissible range, the meniscus 12 is controlled to be within the permissible range by controlling the pressure acting on the liquid agent tank 2 (step S10), and the procedure from step S1 is repeated.

  Here, a control method of the pressure control unit 3 that controls the pressure applied to the liquid agent tank 2 will be described. In the present embodiment, as shown in FIG. 6A, when the amount of liquid forming the meniscus 12 is large and the dimension A (or the predetermined angle) is large (or when the angle θb is small), The difference value between the predetermined dimension A (or predetermined angle) or the area value of the meniscus 12 and the preset value stored in advance is calculated, and the negative value applied to the liquid agent tank 2 so as to fall within the predetermined dimension value / angle / area value. Is controlled so that the amount of liquid at the tip of the inkjet head 1 is drawn into the liquid agent tank 2 side. On the contrary, as shown in FIG. 8A, when the amount of liquid forming the meniscus 12 is small and the dimension A (or the predetermined angle) is small (or when the angle θb is large), the liquid agent tank 2 The negative pressure to be applied is controlled to be small, and the liquid amount of the liquid 11 at the tip of the inkjet head 1 is controlled to be large by utilizing the water head difference. As a result, the distance A and the angle θa or the angle θb of the meniscus 12 or the area value of the meniscus 12 are controlled within the allowable range. As a means for controlling the pressure, it is preferable to use a vacuum pump or an ejector device that can draw air, but the invention is not limited to this.

FIG. 10 is an example showing the flow of another control operation. In addition to the procedure of FIG. 9, the stable discharge state can be obtained more reliably by checking in the preliminary discharge state.
First, the step of comparing the current meniscus 12 shape from step S1 to step S3 with the optimal meniscus 12 shape stored in advance is the same. After the current meniscus 12 shape is within the allowable range (step S3), preliminary ejection is performed (step S4). The number of droplets discharged in the preliminary discharge may be one or a plurality of droplets. The meniscus 12 at that time is imaged (step S5), and a predetermined dimension (area value) of the imaged meniscus 12 at the time of ejection is measured (step S6), and compared with the meniscus 12 at the time of non-ejection (step S7). If the compared value is within the allowable range, the process proceeds to the step of discharging to the target medium 5 (step S8). However, if it is out of the allowable range, the pressure applied to the liquid agent tank 2 is controlled in step S10 to control the shape of the meniscus 12 to obtain an optimum discharge state.

  Further, as another criterion for judgment, when image processing is performed on the meniscus 12 at the time of ejection in step S6, it is judged whether or not an optimum ejection state is obtained by recognizing the position of the ejected droplet 4. May be. For example, when only one droplet is ejected at the time of preliminary ejection, an image of the droplet 4 at the time of continuous ejection is stored in advance, and the state and the position / size of the droplet 4 are compared, so that the optimum It may be determined whether or not the discharge state is obtained. The position / size / satellite presence / absence changes depending on the state of the meniscus 12 during non-ejection. Also, when the number of ejected droplets at the time of preliminary ejection is plural, if the shape of the meniscus 12 is not optimal, as shown in FIGS. 7 (a) and 7 (b), a plurality of droplet images are captured from the first droplet. The position of the droplet changes to the eyes, and the image of the droplet 4 is blurred. For example, FIG. 7A shows a case where the amount of liquid forming the meniscus 12 is large, and FIG. 7B shows a case where the amount of liquid forming the meniscus 12 is small. The phenomenon is that the position of the first droplet 4a is different from the droplet position 4e at the time of continuous ejection, and the position of the droplet 4a from the first droplet 4a to the droplets 4b to 4e is changed as the droplet 4 is ejected. It changes and settles in the droplet position 4e which is a stable discharge state. This phenomenon can be confirmed with 3 to 5 drops during preliminary ejection. In the case of the optimum meniscus 12, the positions of the droplets 4a to 4e are almost unchanged. In step S5, an image of the preliminary discharge may be captured, and it may be determined in step S7 whether or not the optimum discharge from the first drop by the meniscus 12 is obtained.

  Here, Table 1 shows an example of an experiment in the present embodiment.

これは、本実施の形態の中で使用した前述のインクジェットヘッド１および水を溶媒とする、ある液剤１１において、撮像部７および画像処理部９により処理したインクジェットヘッド１先端から凸形状をなすメニスカス１２先端までの距離（膨出寸法）Ａを変更した時の一滴目の液滴半径と、連続吐出時との液滴位置の差異・一滴目吐出と連続吐出のそれぞれの挙動・吐出状態の判定を示したものであり、最下段は安定した吐出状態である連続吐出時の液滴半径および挙動を示している。なお、液滴位置の差異とは連続吐出時の液滴位置を０とし、吐出一滴目の液滴位置との差異（前記距離Ｚ）を示しており、インクジェットヘッド１先端に近づく側を−、インクジェットヘッド１先端より遠ざかる側を＋とした。インクジェットヘッド１先端からメニスカス１２先端までの距離（膨出寸法）Ａが１５〜２０μｍの時は液滴半径も液滴位置も連続吐出時とほぼ変わらず、吐出状態も一滴目・連続吐出とも安定している。

This is a meniscus having a convex shape from the tip of the inkjet head 1 processed by the imaging unit 7 and the image processing unit 9 in a certain liquid 11 using the inkjet head 1 and water as a solvent used in the present embodiment. 12 Dispense radius of the first drop when the distance (bulging dimension) A to the tip is changed and the position of the drop from the continuous discharge, the behavior of the first drop and the continuous discharge, judgment of the discharge state The bottom row shows the droplet radius and behavior during continuous ejection, which is a stable ejection state. The difference in droplet position is defined as a difference (the distance Z) from the droplet position of the first droplet of discharge when the droplet position during continuous ejection is 0, and the side closer to the tip of the inkjet head 1 is −, The side away from the tip of the ink jet head 1 is defined as +. When the distance (bulging dimension) A from the tip of the inkjet head 1 to the tip of the meniscus 12 is 15 to 20 μm, the droplet radius and the droplet position are almost the same as those during continuous ejection, and the ejection state is stable for both the first droplet and the continuous ejection. is doing.

  On the other hand, when the distance A between the leading end of the inkjet head 1 and the leading end of the meniscus 12 is increased, the droplet radius of the first droplet gradually increases and the droplet position approaches the inkjet head 1. When the distance A is further increased, the discharge state becomes unstable. On the other hand, when the distance A between the tip of the inkjet head 1 and the tip of the meniscus 12 is shortened, the droplet radius of the first droplet is slightly reduced, and the droplet position is further away from the inkjet head 1. In the most prominent case, the effect of drying of the liquid 11 and the air pressure at the tip of the inkjet head 1 is increased, and the behavior of generation of satellites and formation of the meniscus 12 becomes unstable. This tendency is observed even during continuous discharge, and the discharge direction of the droplets 4 becomes unstable. In this embodiment, the distance A with a determination of ◯ was slightly different from 15 to 20 μm, and it was determined to be Δ because satellites began to appear and the tendency of the droplet position to change was observed. In addition, the case where the droplet position and the droplet radius were greatly different or the ejection state was not stable was determined as x.

  As described above, in the present invention, the imaging unit 7 that can image the tip of the inkjet head 1 at the standby position is arranged, and the convex meniscus 12 formed at the tip of the inkjet head 1 imaged by the image processing unit 9. By comparing the value of the meniscus 12 stored and set in advance and calculating a difference value, and controlling the pressure applied to the liquid agent tank 2 by the pressure control unit 3, the control is performed to the optimal convex meniscus 12, A stable discharge state can always be obtained from the first drop in which the liquid 11 is discharged from the inkjet head 1.

  In the present embodiment, since the tip of the inkjet head 1 and the convex meniscus 12 to be formed can be visualized, liquid leakage as shown in FIG. 11B can be prevented, and the viscosity of the liquid 11 due to environmental changes. Thus, it is possible to flexibly cope with changes in the meniscus 12 due to changes in characteristics such as changes in the remaining amount of the liquid 11.

Moreover, it can be evaluated by non-ejection, and even if preliminary ejection is required, it can be evaluated with a very small ejection amount, and the consumption of the liquid 11 can be reduced.
Further, by controlling the pressure applied to the liquid agent tank 2 by the pressure control unit 3, there is less influence of noise and harmonics and less possibility of unexpected liquid leakage compared to the method of changing the driving voltage applied to the piezoelectric ceramic. .

  The present invention can be widely used in a droplet discharge method and a droplet discharge apparatus for discharging a liquid agent using an inkjet head.

1 is an overall perspective view of a droplet discharge device according to an embodiment of the present invention. Side view schematically showing the main part of the droplet discharge device from the side (A) Cross-sectional view showing an example of meniscus shape and measurement dimensions at non-ejection in this embodiment (b) Cross-sectional view showing another example of meniscus shape and measurement dimensions at non-ejection in this embodiment Sectional drawing which showed an example of the meniscus shape at the time of discharge in this Embodiment, and a measurement dimension (A) Cross-sectional view for explaining the optimum meniscus shape at the time of non-ejection in the present embodiment (b) Cross-sectional view for explaining the first droplet of ejection at the optimum meniscus shape in the present embodiment (c) ) Cross-sectional view for explaining the continuous discharge at the optimum meniscus shape in the present embodiment (A) Cross-sectional view for explaining a state where the amount of meniscus at the time of non-ejection is large in the present embodiment (b) Cross-sectional view for explaining the first droplet of ejection when the amount of meniscus is large in the present embodiment. c) A cross-sectional view for explaining the continuous discharge when the meniscus amount is large in the present embodiment. (A) Cross-sectional view for explaining a change in the position of a droplet from the first droplet with a large meniscus amount in this embodiment (b) A droplet from the first droplet with a small meniscus amount in this embodiment Sectional drawing for demonstrating the change of a position (A) Cross-sectional view for explaining a state where the meniscus amount at the time of non-ejection is small in the present embodiment (b) Cross-sectional view for explaining the first drop of ejection when the meniscus amount is small in the present embodiment. c) Cross-sectional view for explaining the continuous discharge when the meniscus amount is small in the present embodiment An example of a flowchart showing a flow of control operation of the droplet discharge control method according to the present embodiment An example of another flowchart showing the flow of the control operation of the droplet discharge control method according to the present embodiment (A) Cross-sectional view for explaining a meniscus controlled to be negative in the axial direction of the nozzle head in the conventional droplet discharge control method. (B) For explaining liquid leakage in the conventional droplet discharge control method. Cross section Sectional drawing for demonstrating the meniscus state controlled when changing the amount of discharge droplets in the inkjet nozzle head of another conventional droplet discharge control method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet nozzle head 2 Liquid agent tank 3 Pressure control part 4 Droplet 5 Target medium (target object)
6 Head holder 7 Imaging unit (image capturing unit)
9 Image processing unit 10 Control device 11 Liquid agent 12 Meniscus

Claims (10)

A droplet discharge control method for discharging a liquid agent from an inkjet head,
A droplet discharge control method for controlling the liquid agent meniscus at the tip of the inkjet head before discharging the first droplet to have a convex shape.   The droplet discharge control according to claim 1, wherein the meniscus of the liquid agent at the tip of the inkjet head before discharging the first droplet is made to have a predetermined convex shape by controlling the pressure to the liquid agent tank that supplies the liquid agent to the inkjet head. Method.   The droplet discharge control method according to claim 2, wherein a liquid meniscus is photographed at a tip portion of the ink jet head, and the pressure to the liquid agent tank is controlled based on a photographed image of the meniscus.   The liquid meniscus is imaged at the tip of the ink jet head, and the pressure to the liquid agent tank is controlled based on the bulge size of the photographed image of the meniscus, the bulge angle at a predetermined location, or the bulge area. Droplet discharge control method. The bulge size or bulge area that bulges from the tip of the inkjet head based on the captured image of the meniscus, or the inclination angle with respect to the side end surface of the tip of the inkjet head at a specific location is set to a preset bulge size or setting. Compared with the bulging area or the set inclination angle,
If the bulge size or bulge area of the captured image of the meniscus is larger than the set bulge size or set bulge area, or if the tilt angle of the captured image of the meniscus is smaller than the set tilt angle, the pressure of the liquid agent tank Control to decrease,
If the bulge size or bulge area of the meniscus photographed image is smaller than the set bulge dimension or bulge area, or the tilt angle of the photographed image is larger than the set tilt angle, the pressure of the liquid tank is increased. The droplet discharge control method according to claim 4, wherein the droplet discharge control method is controlled so as to be performed.   The liquid according to claim 1, wherein the liquid meniscus at the tip of the inkjet head before discharging the first droplet is controlled so as to have a convex shape similar to the state immediately before discharge in the continuous discharge state. Drop ejection control method.   5. The droplet discharge control method according to claim 3, wherein the pressure of the liquid agent tank is controlled based on a photographed image of the meniscus of the liquid agent at the tip portion of the ink jet head taken at the time of preliminary discharge. An inkjet head for discharging the liquid agent;
A liquid tank for supplying the liquid to the inkjet head;
A pressure control unit for controlling a tank pressure to the liquid agent tank;
An image photographing unit for photographing the meniscus of the liquid agent at the tip of the inkjet head and outputting the image signal;
A droplet discharge device comprising: a control device that outputs a pressure control unit command signal for controlling the pressure control unit based on image information of a meniscus that bulges from a tip of the inkjet head.   The control means is a liquid agent at the tip of the inkjet head according to a bulge size or bulge area bulged from the tip of the inkjet head based on a captured image of the meniscus, or an inclination angle with respect to a side end surface of the tip of the inkjet head at a specific location. The droplet discharge device according to claim 8, wherein the meniscus is controlled to have a predetermined shape. The control means
The bulge size or bulge area that bulges from the tip of the inkjet head based on the captured image of the meniscus, or the inclination angle with respect to the side end surface of the tip of the inkjet head at a specific location is set to a preset bulge size or setting. Compared with the bulging area or the set inclination angle,
If the bulge size or bulge area of the captured image of the meniscus is larger than the set bulge size or the set bulge area, or smaller than the set inclination angle, control is performed to reduce the pressure of the liquid agent tank,
If the bulge size or bulge area of the meniscus photographed image is smaller than the set bulge dimension or bulge area, or the tilt angle of the photographed image is larger than the set tilt angle, the pressure of the liquid tank is increased. The droplet discharge device according to claim 9, wherein the droplet discharge device is controlled so as to be controlled.

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