CN113978121A - Liquid droplet observation device and liquid droplet observation method - Google Patents

Abstract

The present disclosure provides a droplet observation apparatus and a droplet observation method. A droplet observation device (200) is provided with: a measurement unit (251) that measures, based on an image of a droplet, a first dimension (L1) and a second dimension (L2), the first dimension (L1) being a dimension of an extension (104) of the droplet (101) and being a dimension in a direction of movement of the droplet (101), the second dimension (L2) being a dimension of a thin portion (105) in the direction of movement, the thin portion (105) being a portion of the extension (104) and being a portion having a dimension in a direction perpendicular to the direction of movement that is shorter than other portions of the extension (104); and a determination unit (252) that determines whether or not the mist (103) caused by the liquid droplets (101) is generated, based on the first dimension (L1) and the second dimension (L2) that are measured.

Description

Liquid droplet observation device and liquid droplet observation method

Technical Field

The present disclosure relates to a droplet observation device and a droplet observation method.

Background

Among the inkjet heads, there is an inkjet head using a piezoelectric element. In the inkjet head of this aspect, the volume of the ink chamber in which the ink is stored is changed by the volume change of the piezoelectric element, and the ink is ejected as droplets.

In order to keep the quality of a printed image obtained by the printing process using the inkjet head of this type constant, the volume, ejection speed, and ejection angle of the droplets of ink ejected from the inkjet head need to be stabilized.

Patent document 1 discloses a measurement device including: the ink is ejected onto the receiving member, dots formed on the receiving member are photographed by a camera, and the density of the photographed dots is measured, thereby measuring the ejection amount of the ink from the inkjet head (that is, the volume of droplets of the ink).

Patent document 2 discloses an observation device that observes droplets of ink ejected from an inkjet head by imaging the droplets of ink using an imaging device and a light source device.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 9-48111

Patent document 2: japanese patent No. 6524407

Disclosure of Invention

A liquid droplet observation device according to an aspect of the present disclosure includes: a measurement unit that measures, based on an image of a droplet, a first dimension that is a dimension of an extension portion of the droplet and is a dimension in a movement direction of the droplet, and a second dimension that is a dimension in the movement direction of a thin portion that is a portion of the extension portion and is a portion having a dimension in a direction perpendicular to the movement direction that is shorter than other portions of the extension portion; and a determination unit configured to determine whether or not the mist due to the liquid droplets is generated based on the first and second sizes.

A droplet observation method according to an aspect of the present disclosure includes: a step of measuring, based on an image of a droplet, a first dimension that is a dimension of an extension portion of the droplet and is a dimension of a moving direction of the droplet, and a second dimension that is a dimension of a thin portion in the moving direction, the thin portion being a portion of the extension portion and a portion having a dimension in a direction perpendicular to the moving direction shorter than other portions of the extension portion; and determining whether or not the mist due to the droplets is generated based on the first size and the second size that are measured.

Drawings

Fig. 1A is a diagram for explaining generation of mist due to droplets of ink ejected from an inkjet head.

Fig. 1B is a diagram for explaining generation of mist due to droplets of ink ejected from an inkjet head.

Fig. 1C is a diagram for explaining generation of mist due to droplets of ink ejected from the inkjet head.

Fig. 1D is a diagram for explaining generation of mist due to droplets of ink ejected from the inkjet head.

Fig. 1E is a diagram for explaining generation of mist due to droplets of ink ejected from the inkjet head.

Fig. 2 is a diagram showing the overall configuration of a droplet observation device according to an embodiment of the present disclosure.

Fig. 3 is a schematic view showing an ink jet head provided in a droplet observation device according to an embodiment of the present disclosure.

Fig. 4 is a diagram illustrating a functional configuration of a control device provided in the droplet observation device according to the embodiment of the present disclosure.

Fig. 5 is a flowchart showing operations performed by the droplet observation device according to the embodiment of the present disclosure.

Fig. 6 is a diagram showing an example of an image generated by the droplet observation device according to the embodiment of the present disclosure.

Fig. 7 is a diagram showing the results of an experiment for examining the presence or absence of mist generation.

Fig. 8 is a diagram showing physical properties of inks used in the experiment.

Fig. 9 is a graph showing the experimental results.

Description of the symbols

100 nozzle

101 droplet

102 main droplet

103 fog

104 extension part

105 thin part

200 liquid drop observation device

201 control device

250 storage part

251 measurement unit

252 determination unit

220 light source

223 illumination optical system

221 image pickup unit

222 image pickup optical system

210 ink jet head

211 nozzle part

212 nozzle face

L1 first dimension

L2 second dimension

Detailed Description

Whether or not a droplet ejected from an inkjet head is flying normally depends on conditions such as the physical properties of the ink, such as viscosity, surface tension, stringiness, and boiling point, the drive voltage waveform applied to the piezoelectric element, and the resonance period of the pressure wave. Wherein the pressure wave is generated by applying a driving voltage to the piezoelectric element. The resonance period depends on the configuration of the ink chamber.

In order to properly eject the liquid droplets from the inkjet head, it is necessary to properly adjust the various conditions described above. Therefore, in order to maintain the quality of a printed image by an inkjet head shipped as a commercial product to a certain level or more, it is necessary to inspect the manufactured inkjet head before shipping the inkjet head, in addition to the volume, ejection speed, and ejection angle of the droplets of ink ejected from the inkjet head.

When a printing process is performed by an inkjet head, the generation of mist is a cause of failure to obtain a high-quality image. The mist has a very small volume and a slow moving speed, and is strongly affected by air resistance and the like. Therefore, it is very difficult to spray the mist at a desired position.

Therefore, in order to maintain the quality of a printed image by an inkjet head shipped as a product to a certain level or more, it is necessary to inspect the produced inkjet head for the occurrence of mist and sort shipping objects based on the inspection result. In addition, in the evaluation of the ejection characteristics of new ink, if the drive voltage waveform for ejecting ink is not appropriate, mist is also generated. Therefore, when a new ink is used, it is necessary to adjust the drive voltage waveform using the droplet observing apparatus.

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 or not the fog is generated because the fog is very small as described above.

In view of the above circumstances, an object of the present disclosure is to provide a droplet observation device and a droplet observation method capable of quickly and easily detecting whether or not mist is generated.

(principle of mist generation)

First, the principle of generation of the mist 103 when ink is ejected from the inkjet head 210 will be described with reference to fig. 1A, 1B, 1C, 1D, and 1E. Fig. 1A, 1B, 1C, 1D, and 1E are diagrams for explaining generation of mist 103 due to droplets 101 of ink ejected from the inkjet head 210, and show the vicinity of the nozzle 100 of the inkjet head 210. In the present specification, the droplets of ink may be simply referred to as "droplets".

When the volume of the ink chamber (not shown) of the inkjet head 210 changes due to the volume change of the piezoelectric element, ink is pushed out from the ejection portion of the nozzle 100. As a result, droplets 101 of ink are formed as shown in fig. 1A. The droplet 101 of fig. 1A is in a state where the droplet 101 is constituted by a main droplet 102 which is a site constituting a main part of the droplet 101.

Since the ink has viscosity and elasticity of a certain value or more, the main droplet 102 moves in a state where a part of the droplet 101 is in contact with the ejection portion of the nozzle 100. Therefore, the droplet 101 is stretched in the moving direction as the main droplet 102 moves. As a result, as shown in fig. 1B, an extension 104 is formed between the main droplet 102 and the nozzle 100. The extension 104 is formed from a portion of the ink that forms the main droplet 102. In the following description, the moving direction of the main droplet 102 is sometimes simply referred to as the moving direction.

When the main droplet 102 moves further in the moving direction in a state where 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. As a result, as shown in fig. 1C, the portion of the extension 104 on the nozzle 100 side becomes a thin portion 105 having an elongated shape. The thin portion 105 is a portion of the extension portion 104, and is a portion having a dimension in a direction perpendicular to the moving direction shorter than other portions of the extension portion 104.

When the main droplet 102 moves further in the moving direction, the thin portion 105 is separated from the ejection portion of the nozzle 100, and the ink constituting the thin portion 105 changes to mist 103 in the air as shown in fig. 1D. The magnitude of the velocity component in the moving direction of the mist 103 shown in fig. 1D is relatively large.

When the main droplets 102 move further in the moving direction, the kinetic energy of the mist 103 becomes extremely small, and the mist 103 scatters in various directions. The ink constituting the extension 104 other than the thin portion 105 constitutes the main droplet 102. That is, as shown in fig. 1E, the extension 104 disappears, forming a relatively large main droplet 102.

As described above, the shape of the droplet 101 of ink ejected from the nozzle 100 changes while the droplet moves. Specifically, the state where the droplet 101 is mainly composed of the main droplet 102 (see fig. 1A), the state where the main droplet 102 and the extension 104 having no thin portion 105 are composed (see fig. 1B), and the state where the main droplet 102 and the extension 104 having the thin portion 105 are formed (see fig. 1C) are sequentially shifted. When the thin portion 105 is separated from the discharge portion of the nozzle 100, mist 103 is generated (see fig. 1D). When the fine portion 105 is formed, the mist 103 does not always occur, and the ink forming the fine portion 105 may be a part of the main droplet 102.

(embodiment mode)

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

< Structure >

Fig. 2 is a diagram showing the overall configuration of a droplet observation device 200 according to an embodiment of the present disclosure. The droplet observing apparatus 200 includes an inkjet head 210, a light source 220, an image pickup unit 221, and a control device 201. In fig. 2, the downward direction is the ink ejection direction.

The inkjet head 210 is an ejection device that ejects ink as droplets 101. Fig. 3 is a schematic view showing the inkjet head 210.

The inkjet head 210 includes a nozzle portion 211 at an end in the ink ejection direction. The nozzle portion 211 is formed with a plurality of nozzle holes (not shown) as holes for ejecting ink. The nozzle holes are arranged in 1 row at predetermined intervals in the longitudinal direction of the nozzle 211. The nozzle holes may be arranged in a plurality of rows along the longitudinal direction of the nozzle portion 211. Further, when the nozzle holes are arranged in a plurality of rows, the nozzle holes may be arranged in a zigzag pattern. In fig. 3, reference numeral 212 denotes an end surface (hereinafter referred to as a nozzle surface) of the nozzle 211 facing the discharge direction.

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

The light source 220 is a light emitting device that irradiates the nozzle surface 212 and the droplet 101 with light. The light source 220 includes a light emitting diode (not shown) as a light emitting source and an illumination optical system 223 that adjusts the traveling direction of light. The light source 220 strobes the light emitting diode to emit 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 emission signal from the control device 201. The drive signal will be described in detail later.

The illumination optical system 223 includes a plurality of telecentric lenses. The telecentric lens refracts light emitted from the light emitting diode toward a predetermined direction. The light refracted by the telecentric lens is applied to the nozzle surface 212 and the droplet 101.

The imaging unit 221 is an imaging device that images the droplet 101 and generates an image of the droplet 101. The imaging unit 221 includes an imaging element (not shown) and an imaging optical system 222. The image pickup unit 221 picks up an image of a subject irradiated with light from the light source 220. In the present embodiment, the object is mainly the droplet 101 and the nozzle portion 211.

The image pickup optical system 222 includes a plurality of telecentric lenses and forms an image of a subject on the image pickup device.

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

The control device 201 performs overall control of the droplet observing device 200. The control device 201 generates a drive signal and outputs the drive signal to the inkjet head 210, thereby performing ink ejection control of the inkjet head 210. Further, the control device 201 generates a light emission signal and outputs the light emission signal to the light source 220, thereby performing light emission control of the light source 220.

Fig. 4 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).

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

The CPU reads a predetermined program stored in the ROM, expands the program in the RAM, and executes the expanded program, thereby functioning as the measurement unit 251 and the determination unit 252.

The measurement section 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 determination unit 252 determines whether or not the mist 103 due to the liquid droplets 101 is generated based on the measurement result of the measurement unit 251 and the reference data stored in the storage unit 250. The operation of the measuring unit 251 and the determining unit 252 will be described in detail later.

Further, the controller 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.

The droplet observation device 200 may include a transport unit that transports the printing medium on the side from which the ink is ejected with respect to the inkjet head 210. In this case, the print medium can be printed by scanning the print medium.

< action >

Next, the operation performed by the droplet observation device 200 will be described with reference to fig. 5 and 6. Fig. 5 is a flowchart showing operations 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.

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

Since the piezoelectric element changes its volume at a timing corresponding to the voltage waveform, the ink in the ink chamber is discharged from the nozzle hole to the outside of the inkjet head 210.

Next, the light source 220 strobes the light emitting diode to emit light based on the light emission signal output from the control device 201 (step S2). The light emission signal is a signal indicating the timing of causing the light emitting diode to emit light. The light emission signal is set such that the timing at which the light emitting diode emits light is the timing immediately before the droplet 101 leaves the nozzle portion 211. The timing of lighting the light emitting diode is a timing slightly later than the driving timing of the piezoelectric element.

Next, the image pickup section 221 picks up an image of the droplet 101 (step S3). Light emitted from the light source 220 and illuminating the nozzle surface 212 and the droplet 101 is incident on the imaging unit 221, and the nozzle surface 212 and the droplet 101 are imaged.

Then, the image pickup unit 221 generates an image of the droplet 101 based on the image pickup result (step S4).

Next, the measuring unit 251 measures the size of the extended portion 104 and the size of the thin portion 105 based on the image of the droplet 101 (step S5). The measurement of the size by the measuring 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. In addition, the image of fig. 6 includes a case where only one droplet 101 is ejected from the nozzle portion 211, but the image generated in step S4 may include a case where a plurality of droplets 101 are ejected from the nozzle portion 211.

The measuring portion 251 measures a first dimension L1, the first dimension L1 being the dimension of the elongated portion 104 and being the dimension in the moving direction of the droplet 101. Dimension L1 corresponds to the entire length of extension 104 in the direction of travel. Further, a second dimension L2, which is a dimension in the moving direction of the thin portion 105, is measured.

Next, the determination unit 252 determines whether or not the mist 103 due to the droplets 101 is generated based on the first size L1 and the second size L2 measured by the measurement unit 251 (step S6).

Here, the determination section 252 first calculates L2/L1 as a ratio of the second dimension L2 with respect to the first dimension L1. Then, the determination unit 252 acquires the reference data from the storage unit 250, compares the acquired reference data with the calculated L2/L1, and determines that the mist 103 due to the liquid droplets 101 is generated when L2/L1 is equal to or larger than the reference data. The reference data is a reference value of a ratio of the second size L2 to the first size L1, specifically, 0.35. It is found that the mist 103 is easily generated when L2/LI is 0.35 or more. The reference value is based on the following examples.

Next, the controller 201 causes the display device to display the image of the droplet 101 together 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 is generated" or "fog is not generated" in association with the image generated in step S4, for example. In step S7, control device 201 may display the values of first size L1, second size L2, and ratio L2/L1, together with information indicating the determination result, in association with the image generated in step S4.

If the case where the plurality of droplets 101 are ejected is included in the image generated in step S4, and the droplets 101 whose ratio L2/L1 is 0.35 or more and the droplets 101 whose ratio is less than 0.35 are included, information indicating the determination result and the size L1, the size L2, and the ratio L2/L1 of each droplet 101 may be displayed in correspondence with each droplet 101. Alternatively, when the ratio L2/L1 of at least one droplet 101 of the plurality of droplets 101 included in the image generated in step S4 is 0.35 or more, information indicating that the mist 103 is generated may be displayed. Further, when the ratio L2/L1 of all the droplets 101 included in the image generated in step S4 is less than 0.35, information indicating that the mist 103 is not generated may be displayed.

As described above, the droplet observation device 200 according to the present embodiment measures the first dimension L1 of the extension 104 and the second dimension L2 of the slender portion 105 of the droplet 101, and determines whether or not the mist 103 is generated based on the measurement result. Specifically, the droplet observation device 200 determines that the mist 103 is generated when L2/L1, which is a ratio of the first dimension L1 of the extension 104 and the second dimension L2 of the thin portion 105, is equal to or greater than a reference value of 0.35, and determines that the mist 103 is not generated when L2/L1 is smaller than the reference value of 0.35. Therefore, whether or not the mist 103 is generated can be detected more quickly and easily than when the mist 103 is observed directly.

By inspecting the manufactured inkjet head 210 using the droplet observing apparatus 200, it is possible to determine whether or not the mist 103 is generated when the ink is ejected from the inkjet head 210. Therefore, when the printing process is executed using the inkjet head 210 that is determined not to generate the mist 103 by the inspection of the droplet observing apparatus 200, the mist 103 is not caused to be ejected to an unintended position. Therefore, in the case of performing the printing process 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 electronic products such as industrial products manufactured by printing technology.

< modification example >

The processing of steps S1 to S4 shown in fig. 5 may be repeatedly executed. For example, the processing of steps S1 to S4 may be repeated 27 times in 1 second. In this way, in the case where the processing of steps S1 to S4 is repeated, the timing of causing the light emitting diode to emit light is changed with respect to the timing of driving the piezoelectric element every number of times the processing of steps S1 to S4 is performed. In this case, the image pickup unit 221 picks up images of the droplets 101 generated at timings different from the timings at which the droplets 101 are generated, for the droplets 101 generated at each time step S1. Therefore, a plurality of images representing the state from the generation of the droplet 101 to the separation of the droplet 101 from the nozzle portion 211 are generated.

Since the ink jet head 210 has extremely high ejection reproducibility, when the timing of emitting light from the light source 220 is set to be always delayed by a constant time with respect to the driving timing indicated by the driving signal, the droplet observation device 200 images the droplets 101 located at substantially the same spatial position regardless of how many times the processing shown in fig. 5 is executed. That is, an image in which the droplets are stationary at substantially the same position in space is generated.

Therefore, by arranging images of different droplets 101 in order of a short time from generation of the droplet 101 to image capture, the same situation as when a plurality of images are generated by continuously capturing one droplet 101 can be realized. That is, it is possible to observe the time from when the ink is ejected from the nozzle 211 to form the liquid droplet 101 until the liquid droplet 101 is separated from the nozzle 211.

In the case where the processing of steps S1 to S4 is repeated, the processing shown next is executed after the processing of steps S1 to S4 is executed the determined number of times, instead of the processing of steps S5 to S7. Among the plurality of images of the droplet 101 captured by the imaging unit 221, the measuring unit 251 measures the first size L1 and the second size L2 based on an image captured at the last timing with reference to the timing at which the droplet 101 is formed, with the thin portion 105 in contact with the nozzle portion 211. Then, the determination unit 252 determines whether or not the mist 103 is generated based on the measurement result of the measurement unit 251. Then, the controller 201 displays the image of the droplet 101 to be measured on the display device together with the determination result of the determination unit 252.

It is difficult to image the droplet 101 at the timing when the droplet 101 is just about to leave the nozzle portion 211. However, since the droplet observation device 200 changes the timing of capturing the droplet 101 every time the processes of steps S1 to S4 are performed as described above, it is possible to capture the droplet 101 in a state in which the thin portion 105 is 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.

The droplet observing device 200 may include the CPU functioning as the measuring unit 251 and the determining unit 252 and the storage unit 250, and may not include the inkjet head 210, the light source 220, and the imaging unit 221. That is, the image generating device including the inkjet head 210, the light source 220, and the imaging unit 221 may be a device independent from the droplet observing device 200.

In the above embodiment, the control device 201 executes step S5 and step S6, but the control device 201 may not necessarily execute these steps. In this case, the droplet observation device 200 may execute steps S1 to S4 to cause the image generated in step S4 to be displayed on the display device. Then, the person who performs the inspection of the inkjet head 210 may also measure the first size L1 and the second size L2 based on the displayed image of the liquid droplets 101, calculate the ratio L2/L1, and compare the calculated ratio L2/L1 with 0.35 as a reference value, thereby determining whether the mist 103 is generated.

In the above embodiment, the droplet observation device 200 generates an image indicating that the droplet 101 is about to be separated from the nozzle portion 211, but an image indicating that the droplet 101 has been separated from the nozzle portion 211 (hereinafter, referred to as a flight state image) may be generated together with the image. The state where the droplet 101 is separated from the nozzle 211 is the state of the droplet 101 shown in fig. 1E, and is the state where the droplet 101 flies.

In this case, by changing the timing of emitting light from the light emitting diode with respect to the timing of driving the piezoelectric element every number of times the processing of steps S1 to S4 is performed, it is possible to photograph a situation after the liquid droplet 101 has left the nozzle portion 211. In this case, the droplet observation device 200 repeats the processing of steps S1 to S4, thereby generating a plurality of flight state images corresponding to different timings in addition to a plurality of images from when the droplets 101 are generated to when the droplets leave the nozzle portion 211.

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 determined by measuring the diameter of the droplet 101 assuming the droplet 101 as a sphere. Further, since a plurality of flight state images corresponding to different timings are generated, the measurement unit 251 can obtain the position and time difference of the droplet 101 at each timing based on the plurality of flight state images. Therefore, the measuring section 251 can determine the ejection speed and the ejection angle of the droplet 101 based on the position and the time difference of the droplet 101 at each timing. 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 check whether the mist 103 is generated, and to determine whether the droplet 101 is flying normally based on the volume, the ejection speed, and the ejection angle of the droplet 101.

In addition, the image pickup 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, in the case where the image pickup section 221 is a high-speed camera, the droplet observation device 200 can pick up one droplet 101 a plurality of times between the timing of driving the piezoelectric element and the timing of separating the droplet 101 from the nozzle section 211.

In this case, the image pickup unit 221 picks up one droplet 101 a plurality of times and generates images of a plurality of droplets 101 for the one droplet 101. In step S5, the measuring unit 251 selects the last captured image of the droplet 101 captured by the imaging unit 221, in which the thin portion 105 is in contact with the nozzle portion 211 that ejects the droplet 101. Then, the measuring section 251 measures the first size L1 of the elongated portion 104 and the second size L2 of the slender portion 105 of the droplet 101 shown in the selected image. By imaging the droplet 101 a plurality of times while the droplet 101 is being separated from the nozzle 211 in this manner, it is possible to image the droplet 101 in a state where the thin portion 105 is extended to the maximum extent in the moving direction. Therefore, the determination unit 252 can more accurately determine whether or not the mist 103 is generated.

Similarly, when the imaging unit 221 is a high-speed camera, the droplet observation device 200 may generate a plurality of flight state images together with an image indicating that the droplet 101 is about to leave the nozzle unit 211.

In this case, the image pickup unit 221 picks up the image of the droplet 101 a plurality of times until the droplet 101 leaves the nozzle unit 211, and also picks up the image of the droplet 101 a plurality of times in a state where the droplet 101 leaves the nozzle unit 211 and the droplet 101 does not include the extension 104 at different timings. Thus, in step S4, a plurality of images corresponding to timings different from each other before the droplet 101 exits from the nozzle portion 211 and a plurality of flight state images corresponding to timings different from each other are generated.

In this way, since the flight state image is generated, the measurement unit 251 can measure the volume of the droplet 101. Further, since a plurality of flight state images corresponding to different timings are generated, the measurement unit 251 can determine the ejection speed and the ejection angle of the liquid droplets 101. As a result, it is possible to check whether the mist 103 is generated, and to determine whether the droplet 101 is flying normally based on the volume, the ejection speed, and the ejection angle of the droplet 101.

Further, the determination section 252 does not necessarily have to calculate L2/L1 as the ratio of the second dimension L2 to the first dimension L1, and may calculate the ratio L1/L2 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. When the ratio L1/L2 is 2.86 or less, the determination unit 252 determines that the mist 103 is generated.

(examples)

The inventors investigated the influence of the physical properties of the ink and the nozzle diameter of the inkjet head 210 on the ejection state of the ink through experiments. Specifically, the presence or absence of the mist 103 was examined using a plurality of inks having different physical properties from each other. Further, the presence or absence of the generation of the mist 103 was examined using a plurality of inkjet heads 210 having diameters of nozzle holes (hereinafter referred to as nozzle diameters) different from each other in size. The presence or absence of the generation of the mist 103 is performed by a known observation method.

< ink >

The physical properties of the inks used in the experiments are shown in table 1 of fig. 8.

Inks A, B, A/B and C were used in the experiments. The materials of the inks A, B and C are compounds Ac, Bc, and Cc, respectively.

The compounds Ac, Bc and Cc are organic compounds having a molecular skeleton having a hole transporting function. The molecular weights of compounds Ac, Bc and Cc were 6500, 58000 and 15000, respectively.

The compounds Ac, Bc, and Cc were dissolved in an aromatic organic solvent to prepare inks A, B and C. In the production of the inks A, B and C, the solid content concentrations were adjusted so that the viscosities of the inks A, B and C were the same value. In this experiment, the solid content concentrations of ink A, B and C were adjusted to 9.2 wt%, 1.7 wt%, and 1.0 wt%, respectively, so that the viscosities of ink A, B and C were 3.2mPa · s.

The ink a/B was prepared by mixing the compound Ac and the compound Bc at the same weight ratio. Here, as in the case of inks A, B and C, the solid content concentration of ink a/B was adjusted so that the viscosity became 3.2mPa · s.

The surface tensions of ink A, B, A/B and C were 35.5mN/m, 35.0mN/m, 35.3mN/m and 34.9mN/m, respectively. The surface tension of the inks A, B, A/B and C is determined approximately by the surface tension of the organic solvent that dissolves the compound as the material.

The densities of ink A, B, A/B and C were the same value (951 kg/m)³)。

Further, the inventors determined reynolds number Re, weber number We, olonzeg number On, and Z value Z for ink A, B, A/B and C. In the following description, the reynolds number Re, the weber number We, the inorgo number On, and the Z value Z are collectively expressed as fluid parameters.

< Reynolds number Re >

The reynolds number Re is a dimensionless number represented by a ratio of an inertial force and a viscous force of a fluid, and is a value used for hydrodynamically investigating properties of "flow" of the fluid.

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.

[ mathematical formula 1]

< Weber number We >

The weber number We is a dimensionless number represented by the ratio of the inertial force and the surface tension force. The weber number We is a value important in processing a two-phase flow, and is a value used in the discussion of the behavior of the droplets 101 related to the deformation of the droplets 101 when the droplets 101 flow in a gas flow and the stability of the interface of the droplets 101.

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.

[ mathematical formula 2]

< OnZong number On >

The Olympic lattice number On is a dimensionless number representing the relationship between viscous force, inertial force, and surface tension. The Onezochralski number On is represented by formula (3) using Reynolds number Re and Weber number We.

[ mathematical formula 3]

< Z value Z >

The Z value Z is a dimensionless number represented by the reciprocal of the oin lattice number On and is represented by formula (4).

[ mathematical formula 4]

The reynolds numbers Re, weber numbers We, olonzeg numbers On, and Z values of the inks A, B, A/B and C were determined using the ink densities ρ, the ink viscosities η, the surface tension γ, the diameters r of the ink droplets 101, and the velocities V of the ink droplets 101 shown in the equations (1) to (4) and table 1, respectively.

Since the diameter r of the ink droplet 101 is substantially 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 droplet 101. The velocity V of the ink droplets 101 emitted from the inkjet head 210 is 5 m/s.

< contents of the experiments >

The inventors ejected ink A, B and a/B using an inkjet head 210 having a nozzle diameter of 12 μm, and observed droplets 101 of each ejected ink. Further, inks B and C were ejected using an inkjet head 210 having a nozzle diameter of 18 μm, and droplets 101 of each ejected ink were observed.

The extended portion 104 and the thin portion 105 of the droplet 101 of each ink to be ejected were measured using the droplet observation device 200 according to the above-described embodiment.

< results of the experiment >

Table 2 of fig. 9 shows the nozzle diameter In of the inkjet head 210 used for ejection, the fluid parameters, and the inkjet ejection characteristics of each ink. The ink-jet ejection characteristics include a first size L1 of the elongated portion 104 of the ejected liquid droplet 101, a second size L2 of the thin portion 105, a ratio L2/L1, and a generation condition of the mist 103.

(1) Results of the case where the nozzle diameter In was 12 μm

Since the viscosity η, surface tension γ, density ρ, and other physical properties of the ink a, the ink B, and the inks a/B are substantially the same, the Z values Z of the ink a, the ink B, and the inks a/B are substantially the same.

The value of L2/L1 is from small to large in the order of ink A, ink A/B, and ink B. For example, ink A had L1 of 38 μm, L2 of 12 μm, and L2/L1 of 0.32.

The generation of the mist 103 was not generated in the case of the ink a in which L2/L1 was 0.32. On the other hand, when ink B with L2/L1 being 0.48 and ink a/B with L2/L1 being 0.44, mist 103 is generated.

(2) Results of the case where the nozzle diameter In was 18 μm

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

The ink ejection characteristics are such that the mist 103 is not generated when the ink B is ejected. This result is In contrast to the occurrence of the mist 103 when the ink B is ejected using the inkjet head 210 having a nozzle diameter In of 12 μm.

The Z values Z and L2/L1 of the ink B with the nozzle diameter In of 18 μm were 7.6 and 0.12, respectively.

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

Fig. 7 is a graph summarizing experimental results. Fig. 7 shows the relationship between the Z value of the ink and the values of L2/L1 in each measurement.

From the experimental results, it was found that the presence or absence of the generation of the mist 103 had no relation with the Z value Z. When the second dimension L2 of the thin portion 105 of the droplet 101 of the ink to be ejected is 0.35 or more with respect to the first dimension L1 of the extension portion 104, it is found that the mist 103 is generated.

Therefore, by measuring the dimension L1 of the extension 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 0.35, it is possible to accurately determine whether or not the mist 103 caused by the droplet 101 is generated.

As described above, according to the present disclosure, it is possible to provide a droplet observation device and a droplet observation method capable of quickly and easily detecting whether or not mist is generated.

The above-described embodiments and modifications are merely specific examples for implementing the present disclosure, and the technical scope of the present disclosure is not to be construed as limited by these examples. That is, the present disclosure can be implemented in various forms without departing from the gist or main features thereof.

Industrial applicability

The droplet observation device and the droplet observation method of the present disclosure can be suitably used for determining the generation of mist.

Claims (6)

1. A droplet observation device is provided with:

a measurement unit that measures, based on an image of a droplet, a first dimension that is a dimension of an extension portion of the droplet and is a dimension in a movement direction of the droplet, and a second dimension that is a dimension in the movement direction of a thin portion that is a portion of the extension portion and is a portion having a dimension in a direction perpendicular to the movement direction that is shorter than other portions of the extension portion; and

and a determination unit that determines whether or not the mist due to the liquid droplets is generated based on the first and second sizes that are measured.

2. A droplet observation device according to claim 1,

the determination unit determines that the fog is generated when a ratio of the second size to the first size is 0.35 or more.

3. The liquid droplet observation device according to claim 1 or 2,

further provided with: and an imaging unit that images the liquid droplet to generate an image of the liquid droplet.

4. A droplet observation device according to claim 3,

the image pickup section picks up the liquid droplets a plurality of times,

the measuring unit measures the first size and the second size based on an image that is finally captured by the nozzle unit that ejects the liquid droplet and that is in contact with the thin portion, among the plurality of images of the liquid droplet captured by the imaging unit.

5. A droplet observation device according to claim 3,

the image pickup section picks up a plurality of images of the liquid droplets ejected from the nozzle section,

the measuring unit measures the first size and the second size based on an image that is captured last after the thin portion comes into contact with the nozzle portion and the droplet is formed, among the plurality of images captured by the imaging unit.

6. A droplet observation method comprising:

a step of measuring, based on an image of a droplet, a first dimension that is a dimension of an extension portion of the droplet and is a dimension of a moving direction of the droplet, and a second dimension that is a dimension of a thin portion in the moving direction, the thin portion being a portion of the extension portion and a portion having a dimension in a direction perpendicular to the moving direction shorter than other portions of the extension portion; and

and determining whether or not the mist due to the droplets is generated based on the first and second sizes measured.

Images