Liquid droplet observation device and liquid droplet observation method

Abstract

The present disclosure provides a liquid droplet observation device and a liquid droplet observation method. The liquid droplet observation device (200) comprises: a measuring unit (251) for measuring a first size (L1) and a second size (L2) based on a liquid droplet image, wherein the first size (L1) is the size of an elongated portion (104) of the liquid droplet (101) and is the size in the moving direction of the liquid droplet (101); and the second size (L2) is the size of a thin portion (105) in the moving direction, wherein the thin portion (105) is a portion of the elongated portion (104) and is a portion having a size in a direction perpendicular to the moving direction shorter than other portions of the elongated portion (104); and a judging unit (252) for judging whether mist (103) caused by the liquid droplet (101) is generated based on the measured first size (L1) and second size (L2).

Description

Technical Field

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

[0002] Among inkjet heads, there are those that utilize piezoelectric elements. This type of inkjet head utilizes volume changes of the piezoelectric elements to change the volume of an ink chamber storing ink, thereby ejecting the ink as droplets.

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

[0004] Patent document 1 discloses the following measuring device: ink is ejected onto a receiving part, ink dots formed on the receiving part are photographed using a camera, and the concentration of the photographed ink dots is measured, thereby measuring the amount of ink ejected from the inkjet head (i.e., the volume of the ink droplets).

[0005] Furthermore, Patent Document 2 discloses an observation device that uses an imaging device and a light source device to capture images of ink droplets ejected from an inkjet head and observe the ink droplets.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 9-48111

[0009] Patent Document 2: Japanese Patent No. 6524407 Summary of the Invention

[0010] A droplet observation device according to one embodiment of the present disclosure comprises: a measuring unit for measuring a first size and a second size based on an image of a droplet, wherein the first size is the size of an elongated portion of the droplet and is the size in the moving direction of the droplet, and the second size is the size of a thin portion in the moving direction, wherein the thin portion is a part of the elongated portion and is a part whose size in a direction perpendicular to the moving direction is shorter than that of other parts of the elongated portion; and a judging unit for judging whether mist caused by the droplet will be generated based on the measured first and second sizes.

[0011] A droplet observation method according to one embodiment of the present disclosure includes: a step of measuring a first size and a second size based on an image of the droplet, wherein the first size is the size of an elongated portion of the droplet and is the size in the direction of movement of the droplet, and the second size is the size of a thin portion in the direction of movement, wherein the thin portion is a part of the elongated portion and is a part whose size in a direction perpendicular to the direction of movement is shorter than that of other parts of the elongated portion; and a step of determining whether mist caused by the droplet will be generated based on the measured first size and second size. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1A This is a diagram for explaining the generation of mist caused by ink droplets ejected from an inkjet head.

[0013] Figure 1B This is a diagram for explaining the generation of mist caused by ink droplets ejected from an inkjet head.

[0014] Figure 1C This is a diagram for explaining the generation of mist caused by ink droplets ejected from an inkjet head.

[0015] Figure 1D This is a diagram for explaining the generation of mist caused by ink droplets ejected from an inkjet head.

[0016] Figure 1E This is a diagram for explaining the generation of mist caused by ink droplets ejected from an inkjet head.

[0017] Figure 2 It is a diagram showing the overall structure of a liquid droplet observation device according to an embodiment of the present disclosure.

[0018] Figure 3 It is a schematic diagram showing an inkjet head included in the liquid droplet observation device according to an embodiment of the present disclosure.

[0019] Figure 4 It is a diagram showing the functional configuration of a control device included in the liquid droplet observation apparatus according to an embodiment of the present disclosure.

[0020] Figure 5 This is a flowchart showing the operation performed by the liquid droplet observation device according to the embodiment of the present disclosure.

[0021] Figure 6 This is a diagram showing an example of an image generated by the liquid droplet observation device according to an embodiment of the present disclosure.

[0022] Figure 7 This is a diagram showing the results of an experiment to investigate the presence or absence of fog generation.

[0023] Figure 8This is a graph showing the physical properties of ink used in the experiment.

[0024] Figure 9 It is a graph showing the experimental results.

[0025] Explanation of symbols

[0026] 100 nozzles

[0027] 101 Droplets

[0028] 102 main droplet

[0029] 103 Fog

[0030] 104 extension

[0031] 105 thin part

[0032] 200 Droplet Observation Device

[0033] 201 Control Device

[0034] 250 Storage Department

[0035] 251 Measurement Department

[0036] 252 Judgment Department

[0037] 220 light source

[0038] 223 Illumination Optical System

[0039] 221 Camera Department

[0040] 222 Camera Optical System

[0041] 210 inkjet head

[0042] 211 Nozzle

[0043] 212 Nozzle surface

[0044] L1 first size

[0045] L2 Second size DETAILED DESCRIPTION

[0046] Whether droplets ejected from an inkjet head fly properly depends on factors such as the ink's physical properties, such as viscosity, surface tension, stringiness, and boiling point; the driving voltage waveform applied to the piezoelectric element; and the resonant period of the pressure wave. The pressure wave is generated by the driving voltage applied to the piezoelectric element. The resonant period is determined by the structure of the ink chamber.

[0047] To properly eject droplets from an inkjet head, the various conditions mentioned above must be appropriately adjusted. Therefore, to maintain a certain level of image quality when using a commercially available inkjet head, it is necessary to inspect not only the volume, velocity, and angle of the ink droplets ejected from the inkjet head but also the inkjet head itself before shipment.

[0048] When printing with an inkjet head, the generation of mist can be a major factor in preventing high-quality images. Mist is very small and moves slowly, making it significantly affected by air resistance and other factors. Consequently, it can be very difficult to land the mist where you want it.

[0049] Therefore, to maintain a certain level of image quality when using inkjet heads shipped as commercial products, it is necessary to inspect each manufactured inkjet head for mist generation and sort each product based on the inspection results. Furthermore, when evaluating the ejection characteristics of new ink, mist can also occur if the drive voltage waveform used to eject the ink is inappropriate. Therefore, when using new ink, a droplet observation device is required to adjust the drive voltage waveform.

[0050] When the fog is directly observed using the measuring device of Patent Document 1 or the observation device of Patent Document 2, it is difficult to detect whether fog has occurred because the fog is very small as described above.

[0051] In view of such circumstances, the present disclosure aims to provide a liquid droplet observation device and a liquid droplet observation method that can quickly and easily detect whether or not mist is generated.

[0052] (How fog is generated)

[0053] First, refer to Figure 1A 、 Figure 1B 、 Figure 1C 、 Figure 1D as well as Figure 1E , the principle of generating the mist 103 when the ink is ejected from the inkjet head 210 will be described. Figure 1A 、 Figure 1B 、 Figure 1C 、 Figure 1D as well as Figure 1E This figure is used to explain the generation of mist 103 caused by ink droplets 101 ejected from an inkjet head 210, and shows the vicinity of the nozzle 100 of the inkjet head 210. In this specification, ink droplets may be simply referred to as "droplets".

[0054] When the volume of the ink chamber (not shown) of the inkjet head 210 changes due to the volume change of the piezoelectric element, the ink is squeezed out from the ejection portion of the nozzle 100. As a result, Figure 1A As shown, ink droplets 101 are formed. Figure 1A The droplet 101 is in a state where the droplet 101 is composed of the main droplet 102 which is a portion constituting the main part of the droplet 101 .

[0055] Since the ink has a viscosity and elasticity above a certain value, the main droplet 102 moves while a portion of the droplet 101 is in contact with the ejection portion of the nozzle 100. Therefore, as the main droplet 102 moves, the droplet 101 is stretched in the moving direction. As a result, Figure 1B As shown, an extension 104 is formed between the main droplet 102 and the nozzle 100. The extension 104 is formed by a portion of the ink forming the main droplet 102. In the following description, the moving direction of the main droplet 102 may be simply referred to as the moving direction.

[0056] If the main droplet 102 further moves in the moving direction while the extension portion 104 is in contact with the ejection portion of the nozzle 100, the extension portion 104 is stretched in the moving direction. Figure 1C As shown, the portion of the extension 104 on the nozzle 100 side is an elongated narrow portion 105. The narrow portion 105 is a portion of the extension 104 that is shorter than other portions of the extension 104 in a direction perpendicular to the moving direction.

[0057] If the main droplet 102 moves further in the moving direction, the thin portion 105 leaves the ejection portion of the nozzle 100, as shown in FIG. Figure 1D As shown, the ink constituting the thin portion 105 changes into mist 103 in the air. Figure 1D The magnitude of the velocity component in the moving direction of the mist 103 shown is relatively large.

[0058] If the main droplet 102 moves further in the moving direction, the kinetic energy of the mist 103 becomes extremely small, and the mist 103 scatters in all directions. In addition, the ink forming the elongated portion 104 other than the thin portion 105 forms the main droplet 102. Figure 1E As shown, the extension 104 disappears, forming a relatively large main droplet 102.

[0059] As described above, the shape of the ink droplet 101 ejected from the nozzle 100 changes during its movement. Specifically, the shape of the ink droplet 101 is changed in sequence to a state where the ink droplet 101 is mainly composed of the main droplet 102 (see Figure 1A ), a state consisting of a main droplet 102 and an elongated portion 104 without a narrow portion 105 (refer to Figure 1B ), and the state consisting of the main droplet 102 and the elongated portion 104 formed with the narrow portion 105 (refer to Figure 1C Then, when the thin portion 105 leaves the ejection portion of the nozzle 100, mist 103 is generated (see Figure 1D) In addition, when the thin portion 105 is formed, the mist 103 is not necessarily generated, and the ink forming the thin portion 105 may become a part of the main droplet 102.

[0060] (Implementation Method)

[0061] Hereinafter, embodiments of the present disclosure will be described in detail with appropriate reference to the drawings.

[0062] <Structure>

[0063] Figure 2 : is a diagram showing the overall structure of a liquid droplet observation device 200 according to an embodiment of the present disclosure. The liquid droplet observation device 200 includes an inkjet head 210, a light source 220, an imaging unit 221, and a control device 201. Figure 2 In the figure, the downward direction is the direction in which the ink is ejected.

[0064] The inkjet head 210 is a discharge device that discharges ink as droplets 101 . Figure 3 Schematic diagram showing the inkjet head 210 .

[0065] The inkjet head 210 has a nozzle portion 211 at the end portion in the direction of ejection of the ink. A plurality of nozzle holes (not shown) serving as holes for ejecting the ink are formed in the nozzle portion 211. The nozzle holes are arranged in a row at predetermined intervals along the long side direction of the nozzle portion 211. In addition, the nozzle holes may be arranged in a plurality of rows along the long side direction of the nozzle portion 211. Furthermore, when the nozzle holes are arranged in a plurality of rows, they may be arranged in a zigzag pattern. In addition, Figure 3 Reference numeral 212 denotes an end surface of the nozzle portion 211 facing the ejection direction (hereinafter referred to as a nozzle surface).

[0066] The inkjet head 210 includes a piezoelectric element (not shown) for ejecting ink therein. The piezoelectric element is driven by a drive signal from the control device 201, thereby ejecting ink from a plurality of nozzle holes as droplets 101. The drive signal will be described in detail later.

[0067] 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) as a light source and an illumination optical system 223 that adjusts the direction of light propagation. Under the control of the control device 201, the light source 220 flashes the light-emitting diode. Here, the light source 220 flashes the light-emitting diode based on a light emission signal from the control device 201. The drive signal will be described in detail later.

[0068] The illumination optical system 223 includes a plurality of telecentric lenses. The telecentric lenses refract light emitted from the light emitting diodes and direct it in a predetermined direction. The light refracted by the telecentric lenses is irradiated onto the nozzle surface 212 and the droplets 101 .

[0069] The imaging unit 221 is an imaging device that captures the droplets 101 and generates images of the droplets 101. The imaging unit 221 includes an imaging element (not shown) and an imaging optical system 222. The imaging unit 221 captures an object illuminated by the light source 220. In this embodiment, the objects are primarily the droplets 101 and the nozzle unit 211.

[0070] The imaging optical system 222 includes a plurality of telecentric lenses and forms an image of a subject on an imaging element.

[0071] The imaging unit 221 outputs the image of the generated droplet 101 to the control device 201 .

[0072] The control device 201 controls the entire droplet observation apparatus 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. Furthermore, the control device 201 generates a light emission signal and outputs it to the light source 220, thereby controlling the light emission of the light source 220.

[0073] Figure 4 2 is a diagram showing a functional configuration of the control device 201. The control device 201 includes a storage unit 250 and a CPU (Central Processing Unit) (not shown).

[0074] The storage unit 250 includes a ROM (Read Only Memory) and a RAM (Random Access Memory). The storage unit 250 stores data indicating a benchmark for determining whether mist 103 is generated (hereinafter referred to as benchmark data) and a predetermined program. The benchmark data will be described in detail later.

[0075] The CPU reads out a predetermined program stored in the ROM, expands the program in the RAM, and executes the expanded program, thereby functioning as the measuring unit 251 and the determining unit 252 .

[0076] The measuring unit 251 measures the dimensions of the elongated portion 104 and the thin portion 105 of the droplet 101 based on the image of the droplet 101. The determining unit 252 determines whether mist 103 is generated by the droplet 101 based on the measurement results of the measuring unit 251 and the reference data stored in the storage unit 250. The operations of the measuring unit 251 and the determining unit 252 will be described in detail later.

[0077] Furthermore, the control device 201 causes a display device (not shown) to display the image of the droplet 101 together with the determination result of the determination unit 252 .

[0078] Furthermore, the liquid droplet observation device 200 may include a transport unit for transporting a printing medium on the ink ejecting side of the inkjet head 210. In this case, printing can be performed on the printing medium by scanning the printing medium.

[0079] <Action>

[0080] Next, refer to Figure 5 as well as Figure 6 , the actions performed by the droplet observation device 200 are described. Figure 5 This is a flowchart showing the operation performed by the liquid droplet observation device 200 . Figure 6 3 is a diagram showing an example of an image generated by the liquid droplet observation device 200 .

[0081] 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 indicating the timing for driving the piezoelectric element and is composed of a voltage waveform.

[0082] Since the volume of the piezoelectric element changes at a timing corresponding to the voltage waveform, the ink in the ink chamber starts to be discharged to the outside of the inkjet head 210 through the nozzle holes.

[0083] Next, the light source 220 flashes the light emitting diode (LED) based on the light emission signal output from the control device 201 (step S2). The light emission signal indicates the timing for emitting light from the LED. The light emission signal is set so that the timing for emitting light from the LED is just before the droplet 101 leaves the nozzle portion 211. The timing for emitting light from the LED is slightly later than the driving timing of the piezoelectric element.

[0084] Next, the imaging unit 221 captures an image of the droplet 101 (step S3 ). Light emitted from the light source 220 and irradiating the nozzle surface 212 and the droplet 101 enters the imaging unit 221 , thereby forming an image of the nozzle surface 212 and the droplet 101 .

[0085] Then, the imaging unit 221 generates an image of the droplet 101 based on the imaging result (step S4 ).

[0086] Next, the measuring unit 251 measures the size of the elongated portion 104 and the size of the thin portion 105 based on the image of the droplet 101 (step S5). Regarding the size measurement by the measuring unit 251, it is assumed that the image of the elongated portion 104 and the thin portion 105 are generated in step S4. Figure 6 images for illustration. Figure 6 : is a diagram showing an example of an image of a droplet 101 generated by the droplet observation device 200. Figure 6 The image includes a case where only one liquid droplet 101 is ejected from the nozzle portion 211 , but the image generated in step S4 may also include a case where a plurality of liquid droplets 101 are ejected from the nozzle portion 211 .

[0087] The measuring unit 251 measures a first dimension L1, which is the dimension of the elongated portion 104 and the dimension in the moving direction of the droplet 101. The dimension L1 corresponds to the full length in the moving direction of the elongated portion 104. Furthermore, a second dimension L2, which is the dimension of the thin portion 105 in the moving direction, is measured.

[0088] Next, the determination unit 252 determines whether the mist 103 caused by the droplet 101 is generated based on the first size L1 and the second size L2 measured by the measurement unit 251 (step S6 ).

[0089] Here, the determination unit 252 first calculates L2 / L1, which is the ratio of the second dimension L2 to the first dimension L1. The determination unit 252 then retrieves reference data from the storage unit 250 and compares the retrieved reference data with the calculated L2 / L1. If L2 / L1 is greater than the reference data, the determination unit 252 determines that mist 103 will be generated by the droplets 101. The reference data is a reference value for the ratio of the second dimension L2 to the first dimension L1, specifically 0.35. It can be seen that mist 103 is more likely to be generated when L2 / L1 is greater than 0.35. The basis for this reference value will be explained in the embodiments described below.

[0090] Next, the control device 201 displays the image of the droplet 101 on the display device along with the determination result of the determination unit 252 (step S7). Here, the control device 201 displays information indicating the determination result, such as "fog will be generated" or "fog will not be generated," in association with the image generated in step S4. In step S7, the control device 201 may also display the values ​​of the first size L1, the second size L2, and the ratio L2 / L1, along with the information indicating the determination result, in association with the image generated in step S4.

[0091] If the image generated in step S4 includes a situation where multiple droplets 101 are ejected, and includes both droplets 101 with a ratio L2 / L1 of 0.35 or greater and droplets 101 with a ratio of less than 0.35, information indicating the determination result and the size L1, size 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 of the multiple droplets 101 included in the image generated in step S4 is 0.35 or greater, information indicating that mist 103 will be generated may be displayed. Furthermore, if the ratio L2 / L1 of all droplets 101 included in the image generated in step S4 is less than 0.35, information indicating that mist 103 will not be generated may be displayed.

[0092] As described above, the droplet observation device 200 according to this embodiment measures the first dimension L1 of the elongated portion 104 and the second dimension L2 of the thin portion 105 of the droplet 101, and based on these measurement results, determines whether mist 103 is generated. Specifically, the droplet observation device 200 determines that mist 103 is generated when the ratio L2 / L1 (the first dimension L1 of the elongated portion 104 and the second dimension L2 of the thin portion 105) is greater than a reference value of 0.35. If L2 / L1 is less than the reference value of 0.35, the droplet observation device 200 determines that mist 103 is not generated. Therefore, the generation of mist 103 can be detected more quickly and easily than by directly observing the mist 103.

[0093] By inspecting the manufactured inkjet head 210 using the droplet observation device 200, it is possible to determine whether mist 103 is generated when ink is ejected from the inkjet head 210. Therefore, when printing is performed using an inkjet head 210 that has been determined by the droplet observation device 200 to not generate mist 103, mist 103 will not be sprayed onto unintended locations. Therefore, when printing is performed using the inkjet head 210, high-quality printing can be provided. Consequently, the droplet observation device 200 according to the embodiments of the present disclosure can contribute to the development of printed electronic products, such as industrial products manufactured using printing technology.

[0094] <Modification>

[0095] Alternatively, you can repeat Figure 5 The processing of steps S1 to S4 shown in the figure. For example, the processing of steps S1 to S4 can be repeated at a speed of 27 times per second. In this way, when the processing of steps S1 to S4 is repeated, the timing of making the light-emitting diode emit light is changed relative to the timing of driving the piezoelectric element according to each number of times the processing of steps S1 to S4 is performed. In this case, the camera unit 221 captures the droplet 101 at a timing different from the timing of the generation of the droplet 101 for each different droplet 101 generated when step S1 is performed. Therefore, a plurality of images are generated that represent the situation from the generation of the droplet 101 to the separation of the droplet 101 from the nozzle unit 211.

[0096] The inkjet head 210 has an extremely high ejection reproducibility. Therefore, when the timing of emitting light from the light source 220 is set to be always delayed by a constant time relative to the driving timing indicated by the driving signal, the droplet observation device 200 does not rely on the Figure 5 No matter how many times the process shown is executed, the droplet 101 located at substantially the same spatial position is imaged. In other words, an image is generated in which the droplet remains stationary at substantially the same spatial position.

[0097] Therefore, by arranging the images of different droplets 101 in the order of the shortest time from the formation of the droplet 101 to the image capture, it is possible to achieve the same effect as if a single droplet 101 were captured continuously to generate multiple images. In other words, it is possible to track the time from the moment the ink is ejected from the nozzle 211 to form the droplet 101 until the droplet 101 leaves the nozzle 211.

[0098] When the processes of steps S1 to S4 are repeated, the following processes are performed after the processes of steps S1 to S4 have been executed a predetermined number of times, instead of the processes of steps S5 to S7. Among the multiple images of the droplet 101 captured by the imaging unit 221, the measuring unit 251 measures the first dimension L1 and the second dimension L2 based on the image captured at the last timing, when the thin portion 105 contacts the nozzle 211 and the droplet 101 is formed. The determining unit 252 then determines whether mist 103 has been generated based on the measurement results of the measuring unit 251. The control device 201 then displays the image of the droplet 101 being measured on the display device, along with the determination result of the determining unit 252.

[0099] It is difficult to capture an image of the droplet 101 just before it leaves the nozzle 211. However, as described above, the droplet observation device 200 changes the timing of capturing the image of the droplet 101 each time the processing of steps S1 to S4 is executed. This allows the image of the droplet 101 to be captured with the thin portion 105 stretched to its maximum extent in the direction of movement. Consequently, the determination unit 252 can more accurately determine whether mist 103 is generated.

[0100] Furthermore, the liquid droplet observation apparatus 200 only needs to include a CPU and a storage unit 250 that function as the measuring unit 251 and the determining unit 252, and does not need to include the inkjet head 210, the light source 220, and the imaging unit 221. In other words, the image generation device composed of the inkjet head 210, the light source 220, and the imaging unit 221 may be a device independent of the liquid droplet observation apparatus 200.

[0101] In the above embodiment, steps S5 and S6 are described as being executed by the control device 201. However, this does not necessarily require the control device 201 to execute these steps. In this case, the droplet observation device 200 can execute steps S1 to S4, and display the image generated in step S4 on the display device. A person inspecting the inkjet head 210 can then measure the first and second dimensions L1 and L2 based on the displayed image of the droplet 101, calculate the ratio L2 / L1, and compare this calculated ratio L2 / L1 with a reference value of 0.35 to determine whether mist 103 has been generated.

[0102] In the above embodiment, the droplet observation device 200 generates an image showing the situation of the droplet 101 about to leave the nozzle portion 211, but it is also possible to generate an image showing the situation after the droplet 101 leaves the nozzle portion 211 (hereinafter referred to as a flight state image) together with the image. The situation after the droplet 101 leaves the nozzle portion 211 refers to Figure 1E The state of the droplet 101 shown is a state in which the droplet 101 is in flight.

[0103] 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 processing of steps S1 to S4 is performed, it is possible to capture images of the state of the droplet 101 immediately after it leaves the nozzle 211. In this case, the droplet observation device 200 repeatedly performs the processing of steps S1 to S4, thereby generating multiple images of the state of the droplet 101 from the time it is generated to the time it leaves the nozzle 211, in addition to multiple images of the state of the droplet 101 corresponding to different timings.

[0104] In this way, since the flight status image is generated, the measuring unit 251 can measure the volume of the droplet 101. The volume can be calculated by assuming that the droplet 101 is a sphere and measuring the diameter of the droplet 101. In addition, since multiple flight status images corresponding to different timings are generated, the measuring unit 251 can calculate the position of the droplet 101 at each timing and the time difference based on the multiple flight status images. Therefore, the measuring unit 251 can calculate 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 ​​representing the flight status of the droplet 101, can be calculated. As a result, it is possible to check whether mist 103 is generated, and it is possible to determine whether the droplet 101 is flying normally based on the volume, ejection speed, and ejection angle of the droplet 101.

[0105] Alternatively, the imaging unit 221 may be a high-speed camera. In this case, the liquid droplet observation apparatus 200 does not include the light source 220. Thus, when the imaging unit 221 is a high-speed camera, the liquid droplet observation apparatus 200 can capture multiple images of a single droplet 101 between the time the piezoelectric element is driven and the time the droplet 101 leaves the nozzle 211.

[0106] In this case, the imaging unit 221 captures a single droplet 101 multiple times, generating multiple images of the droplet 101 for that single droplet 101. Furthermore, in step S5, the measuring unit 251 selects the last image captured, from among the multiple images of the droplet 101 captured by the imaging unit 221, in which the thin portion 105 contacts the nozzle 211 ejecting the droplet 101. Based on the selected image, the measuring unit 251 measures the first dimension L1 of the extended portion 104 and the second dimension L2 of the thin portion 105 of the droplet 101 shown in the image. By capturing the droplet 101 multiple times until it separates from the nozzle 211, it is possible to capture the droplet 101 with the thin portion 105 stretched to its maximum extent in the direction of movement. Consequently, the determining unit 252 can more accurately determine whether mist 103 is generated.

[0107] Similarly, when the imaging unit 221 is a high-speed camera, the liquid droplet observation device 200 may generate a plurality of flight state images together with an image showing a state in which the liquid droplet 101 is about to leave the nozzle unit 211 .

[0108] In this case, the imaging unit 221 not only captures the droplet 101 multiple times until it leaves the nozzle 211, but also captures the droplet 101 multiple times at different timings after it leaves the nozzle 211 and does not include the extension portion 104. Thus, in step S4, multiple images corresponding to different timings before the droplet 101 leaves the nozzle 211, as well as multiple images of the droplet 101 in flight corresponding to different timings, are generated.

[0109] By generating a flight status image in this manner, the measurement unit 251 can measure the volume of the droplet 101. Furthermore, by generating multiple flight status images corresponding to different timings, the measurement unit 251 can determine the ejection velocity and ejection angle of the droplet 101. As a result, it is possible to check whether mist 103 is being generated and determine whether the droplet 101 is flying normally based on its volume, ejection velocity, and ejection angle.

[0110] Furthermore, the determination unit 252 does not necessarily need to calculate L2 / L1, which is the ratio of the second dimension L2 to the first dimension L1. Instead, it may calculate the ratio L1 / L2, which is the ratio of the first dimension L1 to the second dimension L2. In this case, the reference data is 2.86, which is the reciprocal of 0.35. Furthermore, the determination unit 252 determines that fog 103 is generated if the ratio L1 / L2 is 2.86 or less.

[0111] (Example)

[0112] The inventors experimentally investigated the effects of the physical properties of ink and the nozzle diameter of the inkjet head 210 on the ink ejection state. Specifically, the presence of mist 103 was investigated using multiple inks with different physical properties. Furthermore, the presence of mist 103 was investigated using multiple inkjet heads 210 with different nozzle diameters (hereinafter referred to as nozzle diameters). The presence of mist 103 was observed using known observation methods.

[0113] <Ink>

[0114] exist Figure 8 Table 1 shows the physical properties of the ink used in the experiment.

[0115] The experiments used inks A, B, A / B, and C. The materials of inks A, B, and C were compounds Ac, Bc, and Cc, respectively.

[0116] Compounds Ac, Bc, and Cc are organic compounds having a molecular skeleton capable of hole transporting. The molecular weights of compounds Ac, Bc, and Cc are 6,500, 58,000, and 15,000, respectively.

[0117] Inks A, B, and C were prepared by dissolving compounds Ac, Bc, and Cc in an aromatic organic solvent. During the preparation of inks A, B, and C, the solids concentrations were adjusted so that the viscosities of inks A, B, and C were the same. In this experiment, the solids concentrations of inks A, B, and C were adjusted to 9.2 wt%, 1.7 wt%, and 1.0 wt%, respectively, resulting in a viscosity of 3.2 mPa·s.

[0118] Ink A / B was prepared by mixing compound Ac and compound Bc at the same weight ratio. Here, as with inks A, B, and C, the solid content concentration of ink A / B was adjusted to a viscosity of 3.2 mPa·s.

[0119] The surface tensions of inks A, B, A / B, and C are 35.5 mN / m, 35.0 mN / m, 35.3 mN / m, and 34.9 mN / m, respectively. The surface tensions of inks A, B, A / B, and C are largely determined by the surface tension of the organic solvent that dissolves the raw material compound.

[0120] The densities of inks A, B, A / B, and C are the same value (951 kg / m 3 ).

[0121] In addition, the inventor determined the Reynolds number Re, Weber number We, Ohnesorge number On, and Z value Z for 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 are collectively referred to as fluid parameters.

[0122] <Reynolds number Re>

[0123] The Reynolds number Re is a dimensionless number representing the ratio of the inertial force to the viscous force of a fluid, and is a value used to investigate the "flow" properties of a fluid in a fluid mechanics manner.

[0124] 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.

[0125] [Mathematical formula 1]

[0126]

[0127] <Weber number We>

[0128] The Weber number We is a dimensionless number represented by the ratio of the inertial force to the surface tension. The Weber number We is an important value when dealing with two-phase flow, and is a value used when discussing the behavior related to the deformation of the droplet 101 during the flow of the droplet 101 in the air stream and the stability of the interface of the droplet 101.

[0129] 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.

[0130] [Mathematical formula 2]

[0131]

[0132] <Ohnesorge number On>

[0133] The Ohnesorge number On is a dimensionless number representing the relationship between the 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.

[0134] [Mathematical formula 3]

[0135]

[0136] <Z value Z>

[0137] The Z value Z is a dimensionless number represented by the reciprocal of the Ohnesorge number On, and is expressed by Equation (4).

[0138] [Mathematical formula 4]

[0139]

[0140] Using equations (1) to (4) and the ink density ρ, ink viscosity η, surface tension γ, ink droplet diameter r, and ink droplet velocity V shown in Table 1, the Reynolds number Re, Weber number We, Ohnesorg number On, and Z value Z of inks A, B, A / B, and C were determined respectively.

[0141] Since the diameter r of the ink droplets 101 is approximately equal to the nozzle diameter In of the inkjet head 210, the nozzle diameter In of the inkjet head 210 used is used as the diameter r of the ink droplets 101. Furthermore, the velocity V of the ink droplets 101 ejected from the inkjet head 210 is 5 m / s.

[0142] <Experimental Content>

[0143] 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 ink droplets 101. Furthermore, they used an inkjet head 210 with a nozzle diameter of 18 μm to eject inks B and C, and observed the ejected ink droplets 101.

[0144] Furthermore, the extended portion 104 and the narrow portion 105 of each discharged ink droplet 101 were measured using the droplet observation device 200 according to the above-described embodiment.

[0145] <Experimental Results>

[0146] exist Figure 9 Table 2 shows the nozzle diameter In of the inkjet head 210 used for ejection, fluid parameters, and inkjet ejection characteristics for each ink. The inkjet ejection characteristics include 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 generation of mist 103.

[0147] (1) Results when the nozzle diameter In is 12 μm

[0148] Ink A, Ink B, and Ink A / B have substantially the same physical properties such as viscosity η, surface tension γ, and density ρ. Therefore, the Z values ​​Z of Ink A, Ink B, and Ink A / B are substantially the same.

[0149] The value of L2 / L1 increases in the order of ink A, ink A / B, and ink B. For example, the value of L2 / L1 of ink A is 38 μm, the value of L2 is 12 μm, and the value of L2 / L1 is 0.32.

[0150] The mist 103 did not occur in the case of ink A with an L2 / L1 ratio of 0.32. On the other hand, the mist 103 occurred in the case of ink B with an L2 / L1 ratio of 0.48 and ink A / B with an L2 / L1 ratio of 0.44.

[0151] (2) Results when the nozzle diameter In is 18 μm

[0152] Since the physical properties of ink B and ink C, such as viscosity η, surface tension γ, and density ρ, are substantially the same, the Z values ​​Z of ink B and ink C are the same value.

[0153] Inkjet Ejection Characteristics: When the ink B was ejected, the mist 103 was not generated. This result is in contrast to the mist 103 generated when the ink B was ejected using the inkjet head 210 having a nozzle diameter In of 12 μm.

[0154] When the nozzle diameter In is 18 μm, the Z value Z and L2 / L1 of the ink B are 7.6 and 0.12, respectively.

[0155] On the other hand, when ink C having the same Z value Z as ink B was discharged, mist 103 was generated. In addition, L2 / L1 when ink C was discharged was 0.36.

[0156] Figure 7 is a graph summarizing the experimental results. Figure 7 ] The relationship between the Z value of the ink and the value of L2 / L1 in each measurement is shown in FIG.

[0157] The experimental results show that the generation of mist 103 has no relationship with the Z value Z. Furthermore, mist 103 is generated when the second dimension L2 of the thin portion 105 of the ejected ink droplet 101 is 0.35 or greater relative to the first dimension L1 of the extended portion 104 .

[0158] Therefore, by measuring the size L1 of the extended portion 104 and the size 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 0.35, it is possible to accurately determine whether the mist 103 caused by the droplet 101 will be generated.

[0159] As described above, according to the present disclosure, it is possible to provide a liquid droplet observation device and a liquid droplet observation method that can quickly and easily detect whether mist is generated.

[0160] The above-mentioned embodiments and modifications are merely examples of specific implementations of the present disclosure, and the technical scope of the present disclosure should not be construed in a limiting manner. That is, the present disclosure can be implemented in various forms without departing from its gist or main features.

[0161] Industrial applicability

[0162] The liquid droplet observation device and liquid droplet observation method disclosed herein can be suitably used to determine the generation of mist.

Claims

1. A droplet observation device comprising: a measuring unit configured to measure a first dimension and a second dimension based on an image of the droplet, the first dimension being a dimension of an elongated portion of the droplet in a moving direction of the droplet, and the second dimension being a dimension of a thin portion in the moving direction, the thin portion being a portion of the elongated portion having a dimension in a direction perpendicular to the moving direction shorter than other portions of the elongated portion; and a determination unit that determines whether mist will be generated by the droplets based on the measured first size and the second size; The image of the liquid droplet is an image that is captured last when the thin portion contacts the nozzle portion that ejects the liquid droplet, among a plurality of images obtained by capturing the liquid droplet a plurality of times.

2. A droplet observation device comprising: a measuring unit configured to measure a first dimension and a second dimension based on an image of the droplet, the first dimension being a dimension of an elongated portion of the droplet in a moving direction of the droplet, and the second dimension being a dimension of a thin portion in the moving direction, the thin portion being a portion of the elongated portion having a dimension in a direction perpendicular to the moving direction shorter than other portions of the elongated portion; and a determination unit that determines whether mist will be generated by the droplets based on the measured first size and the second size; The image of the liquid droplet is an image captured last after the thin portion contacts the nozzle portion and forms the liquid droplet, among a plurality of images obtained by capturing the liquid droplet ejected from the nozzle portion a plurality of times.

3. The liquid droplet observation device according to claim 1 or 2, wherein: The determination unit determines that fog will be generated when the ratio of the second size to the first size is 0.35 or greater.

4. The liquid droplet observation device according to claim 1 or 2, wherein: The device further includes an imaging unit that captures an image of the liquid droplet to generate an image of the liquid droplet.

5. A droplet observation method comprising: a step of measuring a first size and a second size based on the image of the droplet, the first size being the size of an elongated portion of the droplet and being the size in the moving direction of the droplet, and the second size being the size of a thin portion in the moving direction, the thin portion being a portion of the elongated portion and being a portion having a dimension perpendicular to the moving direction shorter than other portions of the elongated portion; and a step of determining whether mist will be generated by the droplets based on the measured first size and second size; The image of the liquid droplet is an image that is captured last when the thin portion contacts the nozzle portion that ejects the liquid droplet, among a plurality of images obtained by capturing the liquid droplet a plurality of times.

6. A droplet observation method comprising: a step of measuring a first size and a second size based on the image of the droplet, the first size being the size of an elongated portion of the droplet and being the size in the moving direction of the droplet, and the second size being the size of a thin portion in the moving direction, the thin portion being a portion of the elongated portion and being a portion having a dimension perpendicular to the moving direction shorter than other portions of the elongated portion; and a step of determining whether mist will be generated by the droplets based on the measured first size and second size; The image of the liquid droplet is an image captured last after the thin portion contacts the nozzle portion and forms the liquid droplet, among a plurality of images obtained by capturing the liquid droplet ejected from the nozzle portion a plurality of times.

Images