JPS648583B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to the spraying of airless spraying, in which highly pressurized liquid is ejected into the air from a small nozzle at high speed to atomize it, such as airless spraying of liquid paint. The present invention relates to a method for monitoring the state of environmental change and a device used in the method.

Conventionally, in airless spraying, a lip-shaped ejection hole is provided at the tip of the nozzle, and the highly pressurized liquid is ejected into the air as a thin film and atomized into particles. A light emitting element such as a light emitting diode is provided on one side of the ejected thin film liquid, and a light receiving element such as a phototransistor is provided on the other side, so that the light emitted from the light emitting element is transmitted through the ejected thin film liquid. A method is known in which the liquid is ejected by a light-receiving element and the amount of light received, that is, changes in the transmittance through the liquid, is used to monitor the ejection status of the liquid.

However, with this monitoring method, there is no possibility of significant changes in the state of liquid ejection, such as when the ejection of liquid has completely stopped or the amount of ejection has drastically decreased due to a cause such as a clogged nozzle. This can only be detected if
It was impossible to detect even the slightest change in the state of the liquid being ejected.

Incidentally, the atomization state in which a thin film of liquid ejected from a nozzle becomes atomized by collision with air is significantly affected by slight changes in the ejection pressure, viscosity, flow rate, etc. of the liquid. Therefore, the conventional monitoring methods described above are insufficient to monitor whether the liquid is in a normal atomization state. It has been desired to establish a monitoring method that can maintain correct conditions.

An object of the present invention is to provide a new method for monitoring the atomization state by detecting such subtle changes in the ejected liquid.

Below, we will explain the process of its establishment.
As shown in the figure, the liquid L is pressurized to high pressure and is ejected into the air at high speed from the nozzle N, which has a lip-shaped flat ejection hole. In zone A, it forms a nearly smooth film, and in subsequent zone B, it vibrates at high speed in a wavy manner due to collision with the air and travels through the air, and at the atomization point C, it splits into fine particles and scatters. do. Looking at this from a two-dimensional perspective, as shown in Figure 1, when moving from the smooth zone A to the wavy zone B, the width of the liquid film rapidly expands and the film thickness decreases significantly, causing the atomization point C. However, looking at the vibration of the liquid film in the undulating zone B, the vibration frequency of the liquid film is It has been experimentally confirmed that the amplitude gradually increases as the amplitude gradually decreases.
Then, when plotting the points where the vibration frequencies of the liquid film in the wavy band B are the same, as shown in Figure 1, the high frequency band, for example 3000 Hz, changes from the smooth band A to the wavy band. B
2500Hz on the outside, and 2000Hz on the outside.
As mentioned above, the frequency of the same frequency band gradually decreases and spreads out in a petal-like pattern, until the edges of the liquid film vibrate at a low frequency of, for example, 1000Hz, causing fog. At the transformation point C, it splits and scatters into the air. The pattern drawn by connecting points where the vibration frequency of the liquid film is the same changes even with extremely slight changes in the ejection pressure, viscosity, flow rate, etc. of the ejected liquid. It has been experimentally confirmed that there is a significant change in the atomization state at this time. Therefore, we focused on the point that it is possible to detect the vibration frequency of the liquid film at any point in this waving band B, and if the change exceeds a certain value, it can be confirmed that a change has occurred in the liquid ejection state. Specifically, by optically detecting this frequency, it is possible to monitor the ejection state of the liquid and, by extension, the atomization state.

Hereinafter, embodiments of the present invention will be described based on FIG. 2.

In the figure, 1 is a nozzle equipped with a lip-shaped flat ejection hole 2 at the tip, and liquid L pressurized to a high pressure is ejected into the air from the ejection hole 2 of the nozzle 1 at a high velocity. Ru. At this time, as described above, the liquid L immediately after being ejected from the ejection hole 2 forms a smooth liquid film in a narrow range, and then vibrates in a undulating manner due to collision with the air, and the vibration frequency decreases. At the same time, the amplitude increases, and eventually it breaks up into fine particles and scatters into the air. Further, elongated air ejection holes 3 and 4 are formed on both sides of the ejection hole 2 of the nozzle 1 in the same direction as the ejection hole 2, and the pressurized air ejected from these air ejection holes 3 and 4 is The air curtains 5 and 6 form the nozzle 2.
The liquid L is formed substantially parallel to each other on both sides of the liquid L jetted from the liquid L. On the outside of one air curtain 5, a first light emitting element 7 such as a light emitting diode is installed at an angle of approximately 45 degrees with respect to the direction in which the liquid L is ejected. The transmitted light is transmitted through the undulating band of the liquid L, and this transmitted light is transmitted through a phototransistor or the like installed outside the other air curtain 6 so that the optical axis is equal to that of the light emitting element 7. The light is received by the light receiving element 8. Further, the second light emitting element 9 is disposed on the same side as the light receiving element 8, and emits light toward approximately the same point where the light emitted from the first light emitting element 7 passes through the liquid L. is emitted, and the light that hits the liquid film and is reflected is received by the light receiving element 8. Further, the light receiving element 8 is connected to an amplifier 10, and this amplifier 10
is connected to a comparison device 11, which in turn is connected to an output device 12.

Next, to explain the operation of this embodiment, the light emitted from the first light emitting element 7 is transmitted through a predetermined point of the liquid film in the waving band and is received by the light receiving element 8. Since the liquid film at that point vibrates in a wavy manner forming a sine curve, its transmittance changes over time. That is,
When the liquid film is almost perpendicular to the transmitted light, its transmittance is maximum and the amount of light received is maximum, whereas when the liquid film is almost parallel to the transmitted light or at a small angle close to it, When the transmittance becomes the minimum, the amount of light received becomes the minimum, and the period of change in the amount of light received coincides with the vibration frequency of the liquid film. That is, an optical signal that changes at the same frequency as the vibration frequency of the liquid film is input to the light receiving element 8, and this optical signal is input to the light receiving element 8.
After the signal is converted into an electrical signal, it is amplified by an amplifier 10 and input to a comparator 11. By the way, if the jetting pressure of this jetting liquid L decreases, or if the liquid L is a paint, the viscosity increases due to a failure of the heater that adjusts the viscosity of the paint, or the jetting of the nozzle 1 If an abnormality occurs such as a decrease in the jet flow rate due to foreign matter clogging the hole 2,
Since the pattern formed by connecting points with the same vibration frequency in the waving band changes, the vibration frequency of the liquid film at the point through which the light emitted from the light emitting element 7 is transmitted also changes. This change is directly input to the amplifier 10 as a change in the frequency of the electric signal converted by the light receiving element 8, and after being amplified by the amplifier 10, is input to the comparator 11. When the change in the frequency of this electrical signal exceeds the permissible frequency range inputted in advance to the comparison device 11, an abnormality detection signal is sent from the comparison device 11 to the output device 12, and this signal is received. Output device 12
stops the injection of liquid L or activates an alarm device or the like.

On the other hand, the light emitted from the second light emitting element 9 is
The light is reflected at a predetermined point on the liquid film and is received by the light receiving element 8, and since the reflection angle changes due to the vibration of the liquid film, the light receiving element 8 receives the light by changing the direction of reflection. The amount of light received changes. Here, since the period of change in the amount of received light matches the vibration frequency of the liquid film, the reflected light from the second light emitting element 9 also changes from the liquid in the same way as the transmitted light from the first light emitting element 7 described above. The light is input to the light receiving element 8 as an optical signal that changes at the same frequency as the vibration frequency of the membrane. Therefore, changes in the vibration frequency of the liquid film can be detected by having the light receiving element 8 receive the light emitted from either the first light emitting element 7 or the second light emitting element 9. By using both in combination and receiving both transmitted light and reflected light at the light receiving element 8, more reliable detection can be achieved. Also, the first
By causing the transmitted light from the light receiving element 7 and the reflected light from the second light emitting element 9 to interfere with each other, and by utilizing this interference, clearer detection becomes possible.

Note that the air curtains 5 and 6 formed by pressurized air ejected from the air ejection holes 3 and 4 are connected to the light emitting elements 7,
As shown in FIG.
Alternatively, the light-receiving element 8 is housed in the protective cylinder 13, and pressurized air supplied from the pressurized air supply pipe 14 connected to one end of the protective cylinder 13 is passed around the light-emitting element 7 or the light-receiving element 8 and ejected from the protective cylinder 13. It may also be possible to prevent fine particles of the liquid L ejected from the nozzle 1 from adhering to the light emitting element 7 or the light receiving element 8.

Furthermore, the light receiving element 8 is not limited to one that receives light and converts it into an electrical signal, such as a phototransistor. The reflected light may be sent to a remote location as an optical signal and converted into an electrical signal by a photoelectric conversion device provided at the remote location.

As specifically explained in the above embodiment,
The method for monitoring the atomization state in airless spraying of the present invention is to irradiate light onto a predetermined position of a thin film of liquid immediately after it has been ejected from a nozzle, and to receive the light that has passed through or reflected from the liquid. The gist is to convert the signal into a signal with a frequency corresponding to the frequency of vibration at a predetermined position, and monitor the atomization state of the liquid based on changes in the frequency of the signal, and to transmit or reflect the liquid. Rather than detecting the ejected state of the liquid based on the intensity of the light, the system detects changes in the wave-like vibrations caused by the collision of the ejected liquid with the air as changes in the frequency of transmitted or reflected light. However, this is converted into a signal and changes in the atomization state are monitored based on changes in the frequency, so extremely small changes in the ejection pressure, viscosity, flow rate, etc. of the ejected liquid can be monitored. This makes it possible to accurately detect the atomization state of the liquid, which is affected by these subtle changes, and has the effect of preventing the generation of coarse particles, for example. .

Further, the atomization state monitoring device in airless spraying of the present invention sandwiches a thin film of liquid immediately after it has been ejected from a nozzle, or attaches a light emitting element to one side of the liquid and displays the liquid emitted from the light emitting element. a light receiving element that receives transmitted or reflected light and converts it into a signal with a frequency corresponding to the frequency of the liquid;
and a comparison device that emits an abnormality detection signal when the frequency of the signal is outside a predetermined range is connected to the light receiving element, and the device is characterized in that when a change in the vibration of the ejected liquid is outside the predetermined range. When this happens, this can be immediately taken out as a signal, which has the effect of ensuring that the method of the invention can be carried out reliably.

[Brief explanation of drawings]

FIG. 1 is a front view and a plan view for explaining the outline of airless spraying. FIG. 2 is a front view and a block diagram showing one embodiment of the present invention. FIG. 3 is a sectional view of a main part showing another embodiment of the present invention. 1: Nozzle, 5, 6: Air curtain, 7: First
8: Light-receiving element, 9: Second light-emitting element, 11: Comparison device, L: Liquid.

Claims (1)

[Claims] 1. Light is irradiated onto a predetermined position of a thin film of liquid immediately after it has been ejected from a nozzle, and the light transmitted through or reflected from the liquid is received to correspond to the frequency of vibration at the predetermined position of the liquid. A method for monitoring an atomization state in airless spraying, comprising converting the signal into a frequency signal and monitoring the atomization state of the liquid based on changes in the frequency of the signal. 2 A light-emitting element is placed between a thin film of liquid immediately after it has been ejected from a nozzle or on one side of the liquid, and the light emitted from the light-emitting element and transmitted through or reflected from the liquid is received and adjusted to the frequency of the liquid. A light-receiving element that converts the signal into a signal of a corresponding frequency is installed, and a comparison device that emits an abnormality detection signal when the frequency of the signal falls outside a predetermined range is connected to the light-receiving element. A monitoring device for the atomization state in air atomization. 3. The atomization state monitoring device in airless spraying according to claim 2, wherein the light receiving element is an optical fiber.