Droplet observation device and droplet observation method

Abstract

To provide a droplet observation device capable of determining whether or not droplets normally fly.SOLUTION: A droplet observation device includes: a control device for allowing a light source to emit light at a timing later than a timing when a piezoelectric element for discharging droplets from a nozzle part is driven; an imaging part for imaging the droplets which are discharged from the nozzle part, are in a state without including an extension part, and are irradiated with the light by the light source; and a measurement part for measuring a volume, a discharge speed and a discharge angle of the droplets, wherein the control device changes a timing when the control device allows the light source to emit light with respect to the timing when the piezoelectric element is driven, every time the piezoelectric element is driven, the imaging part performs imaging plural times at a plurality of different timings at which the control devices allows the light source to emit light, and generates a plurality of flying state images, and the measurement part measures the volume, the discharge speed and the discharge angle of the droplets, from the plurality of flying state images.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a droplet observation device and a droplet observation method. [Background technology]

[0002] Some inkjet heads use piezoelectric elements, which use changes in volume of the piezoelectric element to change the volume of the ink chamber in which the ink is stored, thereby ejecting the ink as droplets.

[0003] In order to maintain a consistent quality of the printed image obtained by a printing process using this type of inkjet head, it is necessary to stabilize the volume, ejection speed, and ejection angle of the ink droplets ejected from the inkjet head.

[0004] Patent document 1 discloses a measuring device that measures the amount of ink ejected from an inkjet head (i.e., the volume of an ink droplet) by ejecting ink onto a receiving member, capturing an image of the ink dots formed on the receiving member with a camera, and measuring the density of the captured ink dots.

[0005] Moreover, Patent Document 2 discloses an observation device that uses an imaging device and a light source device to capture an image of ink droplets discharged from an inkjet and observe the ink droplets. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-48111 [Patent Document 2] Patent No. 6524407 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present disclosure is to provide a droplet observation device and a droplet observation method that can determine whether droplets are flying normally. [Means for solving the problem]

[0008] A droplet observation device according to one aspect of the present disclosure includes a control device that causes a light source to emit light at a timing later than the timing of driving a piezoelectric element that ejects droplets from a nozzle portion, an imaging unit that images the droplet that is ejected from the nozzle portion, is in a state that does not include an extension portion, and is irradiated with light from the light source, and a measurement unit that measures the volume, ejection speed, and ejection angle of the droplet, wherein the control device changes the timing of causing the light source to emit light relative to the timing of driving the piezoelectric element each time the piezoelectric element is driven, the imaging unit captures images multiple times at multiple different timings at which the light source is emitted to generate multiple flight state images, and the measurement unit measures the volume, ejection speed, and ejection angle of the droplet from the multiple flight state images.

[0009] A droplet observation method according to one aspect of the present disclosure includes a control step of causing a light source to emit light at a timing later than the timing of driving a piezoelectric element that ejects droplets from a nozzle portion; an imaging step of imaging the droplet that has been ejected from the nozzle portion, is in a state in which it does not include an extension portion, and is irradiated with light by the light source; and a measurement step of measuring the volume, ejection speed, and ejection angle of the droplet, wherein in the control step, the timing of causing the light source to emit light is changed relative to the timing of driving the piezoelectric element each time the piezoelectric element is driven, and in the imaging step, images are captured multiple times at multiple different timings when the light source is emitted to generate multiple flight state images, and in the measurement step, the volume, ejection speed, and ejection angle of the droplet are measured from the multiple flight state images. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a droplet observation device and a droplet observation method that are capable of determining whether or not droplets are flying normally. [Brief description of the drawings]

[0011] [Figure 1A] FIG. 1 is a diagram for explaining the generation of mist caused by ink droplets ejected from an inkjet head; [Figure 1B] FIG. 1 is a diagram for explaining the generation of mist caused by ink droplets ejected from an inkjet head; [Figure 1C] FIG. 1 is a diagram for explaining the generation of mist caused by ink droplets ejected from an inkjet head; [Figure 1D] FIG. 1 is a diagram for explaining the generation of mist caused by ink droplets ejected from an inkjet head; [Figure 1E] FIG. 1 is a diagram for explaining the generation of mist caused by ink droplets ejected from an inkjet head; [Diagram 2] FIG. 1 is a diagram showing an overall configuration of a droplet observation device according to an embodiment of the present disclosure. [Diagram 3] FIG. 1 is a schematic diagram showing an inkjet head included in a droplet observation device according to an embodiment of the present disclosure. [Figure 4] FIG. 1 is a diagram showing a functional configuration of a control device provided in a droplet observation device according to an embodiment of the present disclosure. [Diagram 5] A flowchart showing an operation performed by a droplet observation device according to an embodiment of the present disclosure. [Figure 6] FIG. 1 is a diagram showing an example of an image generated by a droplet observation device according to an embodiment of the present disclosure. [Figure 7] Figure showing the results of an experiment to investigate whether mist is generated or not DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (Principle of mist generation) First, the principle of how mist 103 is generated when ink is ejected from inkjet head 210 will be described with reference to Figures 1A, 1B, 1C, 1D, and 1E. Figures 1A, 1B, 1C, 1D, and 1E are diagrams for explaining the generation of mist 103 caused by ink droplets 101 ejected from inkjet head 210, and show the vicinity of nozzle 100 of inkjet head 210. In this specification, ink droplets may also be simply referred to as "droplets."

[0013] When the volume of an ink chamber (not shown) of the inkjet head 210 changes due to a change in volume of the piezoelectric element, ink is pushed out from the ejection portion of the nozzle 100. As a result, an ink droplet 101 is formed as shown in Fig. 1A. The droplet 101 in Fig. 1A is in a state where the droplet 101 is composed of a main droplet 102 which is a portion forming the main part of the droplet 101.

[0014] Since ink has viscosity and elasticity at or above a certain value, the main droplet 102 moves while part of the droplet 101 remains in contact with the ejection portion of the nozzle 100. Therefore, as the main droplet 102 moves, the droplet 101 is stretched in the movement direction. As a result, as shown in FIG. 1B, an elongated portion 104 is formed between the main droplet 102 and the nozzle 100. The elongated portion 104 is formed by part of the ink that forms the main droplet 102. In the following description, the movement direction of the main droplet 102 may also be simply referred to as the movement direction.

[0015] When the main droplet 102 continues to move in the movement direction while the elongated portion 104 is in contact with the discharge portion of the nozzle 100, the elongated portion 104 is stretched in the movement direction. As a result, as shown in Fig. 1C, the portion of the elongated portion 104 on the nozzle 100 side becomes a thin portion 105 having an elongated shape. The thin portion 105 is a portion of the elongated portion 104 that is shorter in the dimension perpendicular to the movement direction than other portions of the elongated portion 104.

[0016] As the main droplet 102 moves further in the movement direction, the tapered portion 105 separates from the ejection portion of the nozzle 100, and the ink that constituted the tapered portion 105 turns into mist 103 in the air, as shown in Fig. 1D. The magnitude of the velocity component in the movement direction of the mist 103 shown in Fig. 1D is relatively large.

[0017] As the main droplet 102 moves further in the direction of movement, the kinetic energy of the mist 103 becomes extremely small, and the mist 103 scatters in various directions. Also, the ink constituting the elongated portion 104 other than the thin portion 105 comes to constitute the main droplet 102. That is, as shown in FIG. 1E, the elongated portion 104 disappears, and a relatively large main droplet 102 is formed.

[0018] As described above, the shape of the ink droplet 101 discharged from the nozzle 100 changes as it moves. Specifically, the droplet 101 changes in sequence between a state in which it is mainly composed of the main droplet 102 (see FIG. 1A), a state in which it is composed of the main droplet 102 and an elongated portion 104 without a thin portion 105 (see FIG. 1B), and a state in which it is composed of the main droplet 102 and an elongated portion 104 in which a thin portion 105 has been formed (see FIG. 1C). Then, when the thin portion 105 leaves the discharge portion of the nozzle 100, a mist 103 is generated (see FIG. 1D). Note that when a thin portion 105 is formed, the mist 103 is not necessarily generated, and the ink forming the thin portion 105 may become part of the main droplet 102.

[0019] (Embodiment) Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings as appropriate.

[0020] <Configuration> Fig. 2 is a diagram showing an overall configuration of a droplet observation device 200 according to an embodiment of the present disclosure. The droplet observation device 200 includes an inkjet head 210, a light source 220, an imaging unit 221, and a control device 201. In Fig. 2, the downward direction is the ink ejection direction.

[0021] The inkjet head 210 is a discharge device that discharges ink as droplets 101. FIG.

[0022] The inkjet head 210 includes a nozzle portion 211 at an end in the ink ejection direction. The nozzle portion 211 has a plurality of nozzle holes (not shown) through which the ink is ejected. The nozzle holes are arranged in a line along the longitudinal direction of the nozzle portion 211 at a predetermined interval. The nozzle holes may be arranged in a plurality of lines along the longitudinal direction of the nozzle portion 211. When the nozzle holes are arranged in a plurality of lines, they may be arranged in a staggered pattern. In FIG. 3, 212 denotes an end surface (hereinafter, nozzle surface) of the nozzle portion 211 that faces the ejection direction.

[0023] The inkjet head 210 includes a piezoelectric element (not shown) for ejecting ink therein. The piezoelectric element is driven based on a drive signal from the control device 201, whereby ink is ejected as droplets 101 from a plurality of nozzle holes. The drive signal will be described in detail later.

[0024] The light source 220 is a light-emitting device that irradiates the nozzle surface 212 and the droplets 101 with light. The light source 220 includes a light-emitting diode (not shown) that is a light-emitting source, and an illumination optical system 223 that adjusts the traveling direction of the light. The light source 220 causes the light-emitting diode to emit a strobe light under the control of the control device 201. Here, the light source 220 causes the light-emitting diode to emit light based on a light-emitting signal from the control device 201. The light-emitting signal will be described in detail later.

[0025] The illumination optical system 223 includes a plurality of telecentric lenses. The telecentric lenses refract the light emitted from the light-emitting diodes so that the light is directed in a predetermined direction. The light refracted by the telecentric lenses is irradiated onto the nozzle surface 212 and the droplets 101.

[0026] The imaging section 221 is an imaging device that captures an image of the droplet 101 and generates an image of the droplet 101. The imaging section 221 includes an imaging element (not shown) and an imaging optical system 222. The imaging section 221 captures an image of a subject irradiated with light by the light source 220. In this embodiment, the subject is mainly the droplet 101 and the nozzle portion 211.

[0027] The imaging optical system 222 includes a plurality of telecentric lenses, and forms an image of the subject on the imaging element.

[0028] The imaging unit 221 outputs an image of the generated droplet 101 to the control device 201.

[0029] The control device 201 executes the overall control of the droplet observation device 200. The control device 201 generates a drive signal and outputs it to the inkjet head 210, thereby controlling the ejection of ink from the inkjet head 210. The control device 201 also generates a light emission signal and outputs it to the light source 220, thereby controlling the light emission of the light source 220.

[0030] 4 is a diagram showing the functional configuration of the control device 201. The control device 201 includes a storage unit 250 and a CPU (Central Processing Unit) (not shown).

[0031] The storage unit 250 includes a ROM (Read Only Memory) and a RAM (Random Access Memory). The storage unit 250 stores data (hereinafter referred to as reference data) indicating a criterion for determining whether or not the mist 103 is generated, and a predetermined program. The reference data will be described in detail later.

[0032] The CPU functions as the measurement unit 251 and the determination unit 252 by reading out a predetermined program stored in the ROM, loading it into the RAM, and executing the loaded program.

[0033] The measuring unit 251 measures the dimensions of the elongated portion 104 and the thin portion 105 of the droplet 101 based on an image of the droplet 101. The determining unit 252 determines whether or not mist 103 is generated due to the droplet 101 based on the measurement result by the measuring unit 251 and the reference data stored in the memory unit 250. The operations of the measuring unit 251 and the determining unit 252 will be described in detail later.

[0034] Moreover, the control device 201 causes a display device (not shown) to display an image of the droplet 101 together with the result of the determination by the determination unit 252.

[0035] The droplet observation device 200 may be provided with a transport unit that transports the print medium to the side where the ink is discharged relative to the inkjet head 210. In this case, printing can be performed on the print medium by scanning the print medium.

[0036] <Operation> Next, an operation performed by the droplet observation device 200 will be described with reference to Fig. 5 and Fig. 6. Fig. 5 is a flowchart showing the operation performed by the droplet observation device 200. Fig. 6 is a diagram showing an example of an image generated by the droplet observation device 200.

[0037] First, the inkjet head 210 drives the piezoelectric element based on a drive signal output from the control device 201 (step S1). The drive signal is a signal that indicates the timing for driving the piezoelectric element, and is composed of a voltage waveform.

[0038] The volume of the piezoelectric element changes at a timing corresponding to this voltage waveform, so that ink in the ink chamber starts to flow out of the inkjet head 210 from the nozzle hole.

[0039] Next, the light source 220 causes the light emitting diode to emit a strobe light based on the light emitting signal output from the control device 201 (step S2). The light emitting signal is a signal that indicates the timing at which the light emitting diode is to emit light. The light emitting signal is set so that the timing at which the light emitting diode is to emit light is the timing immediately before the droplet 101 leaves the nozzle portion 211. The timing at which the light emitting diode is to emit light is slightly later than the driving timing of the piezoelectric element.

[0040] Next, the imaging section 221 captures an image of the droplet 101 (step S3). Light that is emitted from the light source 220 and irradiates the nozzle surface 212 and the droplet 101 is incident on the imaging section 221, whereby an image of the nozzle surface 212 and the droplet 101 is formed.

[0041] Then, the imaging section 221 generates an image of the droplet 101 based on the imaging result (step S4).

[0042] Next, the measurement unit 251 measures the dimensions of the elongated portion 104 and the dimensions of the thin portion 105 based on the image of the droplet 101 (step S5). The measurement of dimensions by the measurement unit 251 will be described assuming that the image of FIG. 6 is generated in step S4. FIG. 6 is a diagram showing an example of an image of the droplet 101 generated by the droplet observation device 200. Note that the image of FIG. 6 includes a state in which only one droplet 101 is discharged from the nozzle portion 211, but the image generated in step S4 may include a state in which multiple droplets 101 are discharged from the nozzle portion 211.

[0043] The measuring unit 251 measures a first dimension L1, which is a dimension of the elongated portion 104 in the direction of movement of the droplet 101. The dimension L1 corresponds to the entire length in the direction of movement of the elongated portion 104. In addition, the measuring unit 251 measures a second dimension L2, which is a dimension in the direction of movement of the thin portion 105.

[0044] Next, the determination unit 252 determines whether or not the mist 103 resulting from the droplets 101 is generated based on the first dimension L1 and the second dimension L2 measured by the measurement unit 251 (step S6).

[0045] Here, the determination unit 252 first calculates L2 / L1, which is the ratio of the second dimension L2 to the first dimension L1. Then, the determination unit 252 acquires reference data from the storage unit 250, compares the acquired reference data with the calculated L2 / L1, and determines that the mist 103 caused by the droplet 101 will be generated if L2 / L1 is equal to or greater than the reference data. The reference data is a reference value of the ratio of the second dimension L2 to the first dimension L1, and is specifically 0.35. It is known that the mist 103 is likely to be generated if L2 / L1 is 0.35 or greater. The basis for this reference value will be described in the examples described below.

[0046] Next, the control device 201 causes the display device to display the image of the droplet 101 together with the determination result by the determination unit 252 (step S7). Here, the control device 201 causes information indicating the determination result, such as "mist is generated" or "mist is not generated", to be displayed in association with the image generated in step S4. In step S7, the control device 201 may also display each value of the first dimension L1, the second dimension L2, and the ratio L2 / L1 together with the information indicating the determination result in association with the image generated in step S4.

[0047] If the image generated in step S4 includes a state in which a plurality of droplets 101 are discharged, and includes droplets 101 with a ratio L2 / L1 of 0.35 or more and droplets 101 with a ratio less than 0.35, information indicating the determination result, as well as the dimension L1, dimension L2, and ratio L2 / L1 of each droplet 101 may be displayed in association with each droplet 101. Alternatively, if the ratio L2 / L1 of at least one droplet 101 among the plurality of droplets 101 included in the image generated in step S4 is 0.35 or more, information indicating that mist 103 will be generated may be displayed. Also, if the ratios L2 / L1 of all droplets 101 included in the image generated in step S4 are less than 0.35, information indicating that mist 103 will not be generated may be displayed.

[0048] As described above, the droplet observation device 200 according to this embodiment measures the first dimension L1 of the elongated portion 104 of the droplet 101 and the second dimension L2 of the thin portion 105, and judges whether or not the mist 103 is generated based on the measurement result. Specifically, the droplet observation device 200 judges that the mist 103 is generated when L2 / L1, which is the ratio of the first dimension L1 of the elongated portion 104 and the second dimension L2 of the thin portion 105, is equal to or greater than the reference value of 0.35, and judges that the mist 103 is not generated when L2 / L1 is less than the reference value of 0.35. Therefore, whether or not the mist 103 is generated can be detected more quickly and easily than by directly observing the mist 103.

[0049] By inspecting the manufactured inkjet head 210 using the droplet observation device 200, it can be determined whether or not the mist 103 is generated when ink is discharged from the inkjet head 210. Therefore, when a printing process is performed using the inkjet head 210 that is determined not to generate the mist 103 by the inspection using the droplet observation device 200, the mist 103 will not land at an unintended position. Therefore, when a printing process is performed using the inkjet head 210, high-quality printing can be provided. As a result, the droplet observation device 200 according to the embodiment of the present disclosure can contribute to the development of printed electronics, which creates industrial products using printing technology.

[0050] <Modification> The processes of steps S1 to S4 shown in FIG. 5 may be repeatedly executed. For example, the processes of steps S1 to S4 may be repeated at a speed of 27 times per second. In this way, when the processes of steps S1 to S4 are repeated, the timing of emitting light from the light emitting diode is changed with respect to the timing of driving the piezoelectric element each time the processes of steps S1 to S4 are executed. In this case, the image capturing unit 221 captures the droplets 101 at different timings with respect to the timing of the droplets 101 being generated for each different droplet 101 generated each time step S1 is executed. Thus, a plurality of images showing the state from when the droplet 101 is generated to when the droplet 101 leaves the nozzle unit 211 are generated.

[0051] Since the inkjet head 210 has extremely high ejection reproducibility, when the timing at which the light source 220 emits light is set to be always delayed by a certain time with respect to the drive timing indicated by the drive signal, the droplet observation device 200 captures an image of the droplet 101 located at approximately the same position in space, regardless of how many times the process shown in Fig. 5 has been executed. That is, an image is generated in which the droplet 101 appears stationary at approximately the same position in space.

[0052] Therefore, by arranging images of different droplets 101 in ascending order of the time from when the droplets 101 are generated to when they are captured, it is possible to realize a method that can be regarded as equivalent to generating a plurality of images by continuously capturing images of one droplet 101. In other words, it is possible to observe the state of the droplet 101 over time from when the ink is discharged from the nozzle portion 211 to form the droplet 101 to when the droplet 101 leaves the nozzle portion 211.

[0053] When the processes of steps S1 to S4 are repeated, instead of the processes of steps S5 to S7, the processes of steps S1 to S4 are executed a set number of times, and then the following process is executed. The measurement unit 251 measures the first dimension L1 and the second dimension L2 based on the image captured at the latest timing based on the timing when the droplet 101 is formed and the thin portion 105 is in contact with the nozzle portion 211, among the multiple images of the droplet 101 captured by the imaging unit 221. Then, the determination unit 252 determines whether or not the mist 103 is generated based on the measurement result by the measurement unit 251. Then, the control device 201 causes the display device to display the image of the droplet 101 to be measured together with the determination result by the determination unit 252.

[0054] It is difficult to image the droplet 101 at the timing just before the droplet 101 leaves the nozzle part 211. However, as described above, the droplet observation device 200 changes the timing of imaging the droplet 101 each time the processes of steps S1 to S4 are executed, so that it is possible to image the droplet 101 in a state in which the thin part 105 is fully stretched in the movement direction. Therefore, the determination part 252 can more accurately determine whether or not the mist 103 is generated.

[0055] Note that the droplet observation device 200 only needs to include a CPU functioning as the measurement unit 251 and the determination unit 252, and a storage unit 250, and may not include the inkjet head 210, the light source 220, and the imaging unit 221. That is, an image generating device composed of the inkjet head 210, the light source 220, and the imaging unit 221 may be a device separate from the droplet observation device 200.

[0056] In the above-described embodiment, it has been described that step S5 and step S6 are executed by the control device 201, but they do not necessarily have to be executed by the control device 201. In this case, the droplet observation device 200 may execute steps S1 to S4 and cause the display device to display the image generated in step S4. After that, a person who inspects the inkjet head 210 may measure the first dimension L1 and the second dimension L2 based on the displayed image of the droplet 101, calculate the ratio L2 / L1, and compare the calculated ratio L2 / L1 with a reference value of 0.35 to determine whether or not the mist 103 is generated.

[0057] In the above-described embodiment, the droplet observation device 200 generates an image showing the state of the droplet 101 immediately before it leaves the nozzle portion 211, but in addition to the image, an image showing the state of the droplet 101 after it leaves the nozzle portion 211 (hereinafter, referred to as a flying state image) may be generated. The state of the droplet 101 after it leaves the nozzle portion 211 is the state of the droplet 101 shown in Fig. 1E, and means the state of the droplet 101 flying.

[0058] In this case, by changing the timing of emitting light from the light emitting diode relative to the timing of driving the piezoelectric element each time the processes of steps S1 to S4 are executed, it is possible to capture an image of the droplet 101 after it has left the nozzle portion 211. In this case, by the droplet observation device 200 repeating the processes of steps S1 to S4, in addition to a plurality of images showing the state of the droplet 101 from when it is generated until it leaves the nozzle portion 211, a plurality of flight state images corresponding to different timings are also generated.

[0059] In this way, since the flight state image is generated, the measurement unit 251 can measure the volume of the droplet 101. The volume can be obtained by measuring the diameter of the droplet 101 assuming that the droplet 101 is a sphere. In addition, since a plurality of flight state images corresponding to different timings are generated, the measurement unit 251 can obtain the position of the droplet 101 at each timing and the time difference based on the plurality of flight state images. Therefore, the measurement unit 251 can obtain the ejection speed and ejection angle of the droplet 101 based on the position of the droplet 101 at each timing and the time difference. Therefore, the volume, ejection speed, and ejection angle of the droplet 101, which are values ​​indicating the flight state of the droplet 101, can be obtained. As a result, it is possible to inspect whether the mist 103 is generated and to determine whether the droplet 101 is flying normally based on the volume, ejection speed, and ejection angle of the droplet 101.

[0060] The imaging unit 221 may be a high-speed camera. In this case, the droplet observation device 200 does not include the light source 220. In this way, when the imaging unit 221 is a high-speed camera, the droplet observation device 200 may image one droplet 101 multiple times during the period from the timing at which the piezoelectric element is driven to the timing at which the droplet 101 leaves the nozzle part 211.

[0061] In this case, the image capturing unit 221 captures an image of one droplet 101 multiple times, and generates multiple images of the droplet 101 for the droplet 101. In addition, in step S5, the measurement unit 251 selects an image captured most recently, in which the thin portion 105 is in contact with the nozzle portion 211 that discharges the droplet 101, from among the multiple images of the droplet 101 captured by the image capturing unit 221. Then, based on the selected image, the measurement unit 251 measures the first dimension L1 of the extension portion 104 of the droplet 101 and the second dimension L2 of the thin portion 105 of the droplet 101 shown in the selected image. In this way, by capturing an image of the droplet 101 multiple times until the droplet 101 leaves the nozzle portion 211, it is possible to capture the droplet 101 in a state in which the thin portion 105 is fully extended in the movement direction to the maximum extent. Therefore, the determination unit 252 can more accurately determine whether or not the mist 103 is generated.

[0062] Similarly, when the imaging section 221 is a high-speed camera, the droplet observation device 200 may generate a plurality of flight state images together with an image showing the state of the droplet 101 immediately before it leaves the nozzle section 211.

[0063] In this case, the image capturing unit 221 captures an image of the droplet 101 multiple times before the droplet 101 leaves the nozzle portion 211, and also captures an image of the droplet 101 multiple times at different timings after the droplet 101 leaves the nozzle portion 211 and in a state in which the droplet 101 does not include the extension portion 104. As a result, in step S4, multiple images corresponding to mutually different timings before the droplet 101 leaves the nozzle portion 211 and multiple flight state images corresponding to mutually different timings are generated.

[0064] In this way, a flight state image is generated, so that the measurement unit 251 can measure the volume of the droplet 101. Furthermore, since a plurality of flight state images corresponding to different timings are generated, the measurement unit 251 can obtain the ejection speed and ejection angle of the droplet 101. As a result, it is possible to inspect whether or not mist 103 is generated, and to determine whether or not the droplet 101 is flying normally based on the volume, ejection speed, and ejection angle of the droplet 101.

[0065] The determination unit 252 does not necessarily have to calculate L2 / L1, which is the ratio of the second dimension L2 to the first dimension L1, and may instead calculate the ratio L1 / L2 of the first dimension L1 to the second dimension L2. In this case, the reference data is the reciprocal of 0.35, that is, 2.86. The determination unit 252 determines that the mist 103 is generated when the ratio L1 / L2 is 2.86 or less.

[0066] (Example) The inventors conducted experiments to investigate the influence of the ink properties and the nozzle diameter of the inkjet head 210 on the ink ejection state. Specifically, the presence or absence of mist 103 was investigated using a plurality of inks having mutually different physical properties. In addition, the presence or absence of generation of mist 103 was investigated using a plurality of inkjet heads 210 having mutually different nozzle hole diameters (hereinafter referred to as nozzle diameters). The presence or absence of generation of mist 103 was investigated using a known observation method.

[0067] <Ink> Table 1 shows the physical properties of the inks used in the experiments.

[0068] [Table 1]

[0069] In the experiment, inks A, B, A / B, and C were used. The materials of inks A, B, and C were compounds Ac, Bc, and Cc, respectively.

[0070] Compounds Ac, Bc, and Cc are organic compounds having a molecular skeleton with a hole transport function. The molecular weights of compounds Ac, Bc, and Cc are 6500, 58000, and 15000, respectively.

[0071] Inks A, B, and C were prepared by dissolving compounds Ac, Bc, and Cc in an aromatic organic solvent. When preparing inks A, B, and C, the solid content concentrations were adjusted so that the viscosities of inks A, B, and C were the same. In this experiment, the solid content concentrations of inks A, B, and C were adjusted to 9.2 wt%, 1.7 wt%, and 1.0 wt%, respectively, so that the viscosities of inks A, B, and C were 3.2 mPa s.

[0072] Ink A / B was prepared by mixing compound Ac and compound Bc in the same weight ratio. Here, the solid content of ink A / B was adjusted so that the viscosity was 3.2 mPa s, similar to inks A, B, and C.

[0073] The surface tensions of inks A, B, A / B, and C were 35.5 mN / m, 35.0 mN / m, 35.3 mN / m, and 34.9 mN / m, respectively. The magnitude of the surface tensions of inks A, B, A / B, and C was determined almost entirely by the surface tension of the organic solvent in which the material compounds were dissolved.

[0074] The densities of inks A, B, A / B, and C are the same (951 g / m 3 ) was.

[0075] The inventors also specified the Reynolds number Re, Weber number We, Ohnesorge number On, and Z value Z for the inks A, B, A / B, and C. In the following description, the Reynolds number Re, Weber number We, Ohnesorge number On, and Z value Z may be collectively referred to as fluid parameters.

[0076] <Reynolds number Re> The Reynolds number, Re, is a dimensionless number that represents the ratio of the inertial force to the viscous force of a fluid. It is a value used to investigate the properties of the "flow" of a fluid from a fluid dynamics perspective.

[0077] The Reynolds number Re is expressed by equation (1) using the density ρ of the ink, the viscosity η of the ink, the diameter r of the ink droplet 101, and the velocity V of the ink droplet 101.

[0078]

number

[0079] <Weber number We> The Weber number We is a dimensionless number represented by the ratio of inertial force to surface tension. The Weber number We is an important value when dealing with two-phase flow and is used when discussing the behavior of droplet 101 as it flows through the air current and the stability of the interface of droplet 101.

[0080] The Weber number We is expressed by Equation (2) using the density ρ of the ink, the diameter r of the ink droplet 101, the velocity V of the ink droplet 101, and the surface tension γ of the ink.

[0081] [Number]

[0082] <Ohnesorge number On> The Ohnesorge number On is a dimensionless number indicating the relationship between viscous force, inertial force, and surface tension. The Ohnesorge number On is expressed by Equation (3) using the Reynolds number Re and the Weber number We. [Number]

[0083] <Z value Z> The Z value Z is a dimensionless number represented by the reciprocal of the Ohnesorge number On and is expressed by Equation (4).

[0084] [Number]

[0085] Using Equations (1) to (4) and the density ρ of the ink, the viscosity η of the ink, and the surface tension γ shown in Table 1, as well as the diameter r of the ink droplet 101 and the velocity V of the ink droplet 101, the Reynolds number Re, the Weber number We, the Ohnesorge number On, and the Z value Z of inks A, B, A / B, and C were each specified.

[0086] Since the diameter r of the ink droplet 101 is approximately equal to the nozzle diameter In of the inkjet head 210, the nozzle diameter In of the inkjet head 210 used was used as the diameter r of the ink droplet 101. In addition, the speed V of the ink droplet 101 ejected from the inkjet head 210 was set to 5 m / s.

[0087] <Experiment details> The inventors used an inkjet head 210 with a nozzle diameter of 12 μm to eject inks A, B, and A / B, and observed the ejected droplets 101 of each ink. In addition, the inventors used an inkjet head 210 with a nozzle diameter of 18 μm to eject inks B and C, and observed the ejected droplets 101 of each ink.

[0088] Moreover, the elongated portion 104 and the thin portion 105 of each ejected ink droplet 101 were measured using the droplet observation device 200 according to the embodiment described above.

[0089] <Experimental Results> Table 2 shows the nozzle diameter In of the inkjet head 210 used for ejection, fluid parameters, and the inkjet ejection characteristics of each ink, including the first dimension L1 of the elongated portion 104 of the ejected droplet 101, the second dimension L2 of the thin portion 105, the ratio L2 / L1, and the occurrence of mist 103.

[0090] [Table 2]

[0091] (1) Results when the nozzle diameter In is 12 μm Since ink A, ink B, and ink A / B have approximately the same physical properties such as viscosity η, surface tension γ, and density ρ, the Z values ​​Z of ink A, ink B, and ink A / B were approximately the same.

[0092] The L2 / L1 value was smallest in the order of ink A, ink A / B, and ink B. For example, ink A had an L1 of 38 μm, an L2 of 12 μm, and an L2 / L1 of 0.32.

[0093] The mist 103 did not occur in the case of ink A, where L2 / L1 was 0.32. On the other hand, the mist 103 occurred in the cases of ink B, where L2 / L1 was 0.48, and ink A / B, where L2 / L1 was 0.44.

[0094] (2) Results when the nozzle diameter In is 18 μm Since ink B and ink C have substantially the same physical properties such as viscosity η, surface tension γ, and density ρ, the Z values ​​Z of ink B and ink C were the same.

[0095] Regarding the inkjet ejection characteristics, when ink B was ejected, mist 103 was not generated. This result is in contrast to the result when ink B was ejected using an inkjet head 210 with a nozzle diameter In of 12 μm, in which mist 103 was generated.

[0096] When the nozzle diameter In was 18 μm, the Z value Z and L2 / L1 of ink B were 7.6 and 0.12, respectively.

[0097] On the other hand, when ink C, which has the same Z value Z as ink B, was ejected, mist 103 was generated. Note that when ink C was ejected, L2 / L1 was 0.36.

[0098] The experimental results are summarized in a graph in Figure 7. Figure 7 shows the relationship between the ink Z value and the L2 / L1 value for each measurement.

[0099] The experimental results showed that there is no relationship between the occurrence of mist 103 and the Z value Z. In addition, it was found that mist 103 occurs when the ratio of the second dimension L2 of the thin portion 105 to the first dimension L1 of the elongated portion 104 of the ejected ink droplet 101 is 0.35 or more.

[0100] Therefore, by measuring the dimension L1 of the extension portion 104 and the dimension L2 of the thin portion 105 of the droplet 101, calculating the ratio L2 / L1, and comparing the calculated L2 / L1 with the reference value of 0.35, it is possible to accurately determine whether or not mist 103 will be generated due to the droplet 101.

[0101] The above-mentioned embodiments and modifications are merely examples of the implementation of the present disclosure, and the technical scope of the present disclosure should not be interpreted as being limited by them. In other words, the present disclosure can be implemented in various forms without departing from the gist or main features thereof. [Industrial Applicability]

[0102] The droplet observation device and the droplet observation method of the present disclosure can be used to determine whether or not droplets are flying normally. [Explanation of symbols]

[0103] 100 nozzles 101 Droplet 102 Main droplet 103 Mist 104 Extension part 105 Thin part 200 Droplet Observation Device 201 Control device 250 Storage section 251 Measuring section 252 Judgment section 220 light source 223 Illumination optical system 221 Imaging unit 222 Imaging Optical System 210 Inkjet head 211 Nozzle section 212 Nozzle surface L1 First dimension L2 Second dimension

Claims

1. a control device that causes the light source to emit light at a timing that is later than the timing at which the piezoelectric element that ejects the liquid droplets from the nozzle portion is driven; an imaging unit that images the droplets discharged from the nozzle and irradiated with light by the light source; A measuring unit for measuring the volume, ejection speed and ejection angle of the droplet; Equipped with the control device changes a timing at which the light source emits light with respect to a timing at which the piezoelectric element is driven each time the control device drives the piezoelectric element; The imaging unit captures images a plurality of times at different timings when the light source is emitted to generate a plurality of flight state images, the measurement unit measures a volume, an ejection speed, and an ejection angle of the droplet from the plurality of flight state images; the plurality of flight state images include an image in which the droplet has a main droplet and an extension portion extending in a moving direction of the main droplet, the extension portion being in contact with the nozzle portion and including a thin portion thinner than the extension portion; The generation of mist caused by the droplets is determined based on a ratio of a dimension of the thin portion to a dimension of the elongated portion. Droplet observation device.

2. The droplet observation device according to claim 1 , wherein the plurality of flight state images are images obtained by capturing images of different droplets discharged from the nozzle portion.

3. 3. The droplet observation device according to claim 1, wherein the measurement unit measures the ejection speed and the ejection angle based on the positions of the droplet at the plurality of timings and the time differences between the plurality of timings.

4. a control step of causing the light source to emit light at a timing later than the timing of driving the piezoelectric element that ejects droplets from the nozzle portion; an imaging step of imaging the droplet discharged from the nozzle portion and irradiated with light by the light source; a measuring step for measuring the volume, the ejection velocity and the ejection angle of the droplet; Including, In the control step, a timing at which the light source emits light is changed with respect to a timing at which the piezoelectric element is driven each time the piezoelectric element is driven; In the imaging step, imaging is performed a plurality of times at different timings when the light source is emitted to generate a plurality of flight state images, In the measuring step, a volume, an ejection speed, and an ejection angle of the droplet are measured from the plurality of flight state images; the plurality of flight state images include an image in which the droplet has a main droplet and an extension portion extending in a moving direction of the main droplet, the extension portion being in contact with the nozzle portion and including a thin portion thinner than the extension portion; The generation of mist caused by the droplets is determined based on a ratio of a dimension of the thin portion to a dimension of the elongated portion. Droplet observation method.

5. The method for observing droplets according to claim 4 , wherein the plurality of flight state images are images obtained by capturing images of different droplets discharged from the nozzle portion.

6. 6. The droplet observation method according to claim 4, wherein in the measuring step, the ejection speed and the ejection angle are measured based on the positions of the droplet at the plurality of times and the time differences between the plurality of times.

Images