JPS6087870A - Method and apparatus for detecting clogging of nozzle of airless painting machine - Google Patents

Abstract

PURPOSE:To prevent defective painting by measuring the loudness level of an ultrasonic wave in a specified frequency region in the vicinity of the nozzle of a spray gun while spraying a paint, and detecting the clogging of the nozzle on the basis of the detected value. CONSTITUTION:The loudness level of an acoustic wave generated from a nozzle 2 in >=20kHz frequency region is high when a paint is regularly sprayed from the nozzle 2. Accordingly, the loudness level of the superposed sound added with the sound of a fan 5 and the noise of the factory is high in the vicinity of the nozzle. Meanwhile, when the nozzle 2 is clogged, the loudness level generated from the nozzle 2 in >=20kHz frequency region is decreased and the loudness level of the superposed sound in the same region is consequently decreased. Since a signal current below a predetermined specified value is inputted to a signal generator 8, a detected signal of the clogging of the nozzle is outputted from the signal generator 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting nozzle clogging in an airless coating machine that sprays high-pressure liquid paint from a small-diameter nozzle at high speed to coat an object, and a detection device used to carry out the method.

In recent years, there has been a trend in the painting field to adopt automatic painting systems using airless paint sprayers in order to save labor, but the nozzles of airless paint sprayers are extremely small in diameter.
Depending on the paint used, nozzle clogging may occur frequently, and if it is detected late on an automatic painting line, a large number of coating defects will occur, so there is an urgent need to develop a method that can detect nozzle clogging early. It has become.

By the way, it is known from experience that when paint is sprayed, the paint is ejected from the nozzle at high speed, generating sound waves, and if the nozzle becomes clogged, the volume in the audible range decreases. , regarding the sound waves generated when paint is actually jetted from a nozzle under certain conditions, 0 to
When the sound pressure level was measured over a frequency band of 50 kHz, the sound pressure level ranged from 0 to 10, as shown by characteristic line a in Figure 2.
In the band up to kllz, the sound pressure level gradually increases from 150 dB to 10 dB, and from 10 k) Iz to 40 k
) In the band up to Iz, the sound pressure level is maintained at about -10 dB, and when it exceeds 40 kllz, the sound pressure level shows a characteristic that it gradually decreases.On the other hand, when the nozzle is artificially clogged and measured, , As already shown by the specific line in the same figure, in the band from 0 to 1 kHz, the sound pressure level gradually increases from 140 dB to 130 dB, and reaches 10 kHz.
llz or 630kl (approximately -30d in the band up to z)
The sound pressure level of B is maintained, and the sound pressure level gradually decreases when the frequency exceeds 30 kHz. In particular, in the band of 10 kHz or higher, there is a clear difference in the sound pressure level between when the nozzle is clogged and when the nozzle is clogged. It was confirmed that there was a difference.

Therefore, it is conceivable to pick up the sound waves generated from the nozzle with a microphone and measure the sound pressure level, and detect a clogged nozzle when the measured value falls below a certain value. , there is the sound of an exhaust fan installed in the booth and noise inside the factory, and these are superimposed on the sound waves generated from the nozzle and picked up by a microphone, and the sound pressure level of the superimposed sound is measured. By the way, if we measure the sound pressure level of the fan and other noise in the factory independently, the fan sound will range from 0 to 30, as shown by specific line C in Figure 2.
In the kHz band, the sound pressure level ranges from approximately OdB to 13
The sound pressure level gradually decreases to 0 dB, and when it exceeds 30 kHz, the sound pressure level decreases rapidly.The noise in the factory ranges from 0 to 30 kHz, as shown by characteristic line d in the same figure.
In the band, the sound pressure level is approximately -45 dB, and 3
When the sound pressure level exceeds 011z, the sound pressure level suddenly decreases. For example, when measuring the sound pressure level of superimposed sound in the audible range below 20kl (z), in this band, the sound pressure level of a superimposed sound is The sound pressure level of noise, especially the sound of the fan, is extremely high and accounts for a large proportion of the superimposed sound, so even if the sound pressure level of the sound waves generated from the nozzle decreases, the reduction in the sound pressure level of the entire superimposed row is not as noticeable. As a result of analyzing the characteristic diagram shown in FIG. There is a noticeable difference in the sound pressure level of the sound waves generated from the nozzle depending on whether the nozzle is clogged or not, and the sound pressure level of the fan sound and noise in the factory is low, so the proportion of the superimposed line becomes small. ,
Within this ultrasonic band, we focused on the fact that a decrease in the sound pressure level of the sound wave generated from the nozzle can be clearly detected as a decrease in the sound pressure level of the superimposed sound. This method measures only a specific band within the band, and detects nozzle clogging when the measured value is less than a predetermined value.

EMBODIMENT OF THE INVENTION Hereinafter, one embodiment of the apparatus of the present invention will be described based on the accompanying drawings, and an embodiment of the method of the present invention will be clarified by explaining its operation.

3 is an automatic spray gun that sprays liquid paint, which is pumped by a reciprocating pump 3 such as a plunger pump or a diaphragm, in the form of a mist from a nozzle 2 toward a workpiece a that is intermittently transferred in a booth 4. In synchronization with the transfer of the object to be coated to the cross section of the spray gun 1, an on-off valve (not shown) installed in the spray gun 1 is opened for a certain period of time by the drive of a driving member, and the coating is carried out. is applied, and the sprayed paint is discharged by a fan 5 installed in the booth l.

A microphone 6 is located near the nozzle 2 of the spray gun 1.
is installed, and this microphone 6 has a 30kl
(It has a built-in bandpass filter that blocks sound waves with frequencies other than the band from z to 40kHz, and only 30k of the picked up sound waves are
It is designed to exchange only ultrasonic waves with a frequency of Hz to 40kHz into a signal current, and the reason why the range of 30kllz to 40kllz is specified here is that as shown in Figure 2, in this specific band, clogging occurs. The sound pressure level of the sound waves generated from the nozzle when there is no
In contrast, when the nozzle is clogged, the sound pressure level decreases to below 130 dB, and the difference in the sound pressure level of the sound waves generated from the nozzle depending on whether the nozzle is clogged becomes particularly noticeable. This is because the sound pressure level of noise in the factory drops rapidly, and the proportion of noise in the superimposed line becomes significantly small.A suitable example of this microphone is one with a resonant frequency of 30kHz to 40kHz, and with moisture resistance. An example of this is an ultrasonic ceramic microphone equipped with a piezoelectric ceramic vibrator that has excellent properties.

An amplifier 7 that amplifies the signal current sent out from the microphone 6, and a signal generator 8 that generates a nozzle clogging detection signal when the amplified signal current falls below a predetermined constant amplitude are connected in sequence to the microphone 6. has been
This signal generator 8 is connected in series with the drive member that opens and closes the on-off valve of the spray gun 1, and operates only when the on-off valve is open, and the signal generator 8 generates a signal. Then, the conveyor for the object to be painted a stops, the on-off valve closes, and the spraying of paint stops.
Furthermore, an alarm etc. will sound.

Next, to explain the operation of this embodiment, when the paint is normally sprayed from the nozzle 2, as shown by the characteristic line a in FIG.
The sound pressure level in a specific band from Hz to 40kl (z) is high, so the sound pressure level in the specific band of the superimposed sound of the sound of the fan 5 and the noise in the factory is high near the nozzle 2, When the nozzle 2 becomes clogged, the sound pressure level of the sound waves generated from the nozzle 2 in a specific band decreases, as shown by the characteristic line in Figure 2, and as a result, the sound pressure level of the superimposed sound in a specific band decreases. Since the sound pressure level also decreases, a signal current with an amplitude below a predetermined value is input to the signal generator 8, and a nozzle clogging detection signal is generated from the signal generator 8, and the signal to be painted is detected. When the conveyor stops, the on-off valve closes, stopping paint injection, and an alarm sounds to notify the operator of the nozzle blockage.

In this example, 30kllz to 40kl
Although the range of lz has been specified, similar effects can be obtained in other specific bands within the frequency band of 20 kllz or more.

Furthermore, in this embodiment, an ultrasonic ceramic microbond having a narrow band characteristic with a resonant frequency of 30 kHz to 40 kHz was used as the microphone 6, but a general microphone that only picks up sound waves and converts them into signal current could be used. However, a configuration may also be adopted in which a bandpass filter is connected at the subsequent stage.

As specifically explained by the above embodiments.

The method for detecting nozzle clogging of an airless paint sprayer according to the present invention is to detect 20
The gist of this method is to measure the sound pressure level of ultrasonic waves in a frequency band of kHz or higher, and detect clogging of a nozzle when the measured value becomes below a predetermined value, The sound waves near the nozzle are
20k, where the difference in the sound pressure level of the sound waves generated from the nozzle is clear depending on whether the nozzle is clogged, and the influence of sound waves other than the sound waves generated from the nozzle is extremely small.
Measure only a specific band within the frequency band above llz,
Since nozzle clogging is detected when the measured value is below a certain value, nozzle clogging can be detected early and reliably, and painting defects can be prevented. The nozzle clogging detection device for an airless paint sprayer of the invention is equipped with a sonic wave detection device that converts only ultrasonic waves within a frequency band of 20 kHz or higher into a signal current, including a microphone placed near the nozzle of the spray gun of the airless paint sprayer. , the gist is that an amplifier that amplifies the signal current and a signal generator that generates a nozzle clogging detection signal when the amplified signal current falls below a certain value are sequentially connected to the sonic wave detection device. 6, which has the effect of reliably implementing the above-mentioned method of the invention.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an overview of an embodiment of the apparatus of the present invention, and FIG. 2 is a characteristic diagram showing the relationship between the frequency of various sound waves and the sound pressure level. ] Nispray gun 2: Nozzle 6: Microphone 7
:Amplifier 8:Signal generator Applicant: Asahi Okuma Sangyo Co., Ltd. Agent Patent attorney: Hiroshi Noguchi'tL1 8 No. 2 Tadashi 11

Claims (1)

[Claims] l The sound pressure level of ultrasonic waves in a frequency band of 20 kHz or more is measured in the vicinity of the nozzle of the spray gun during paint injection, and when the measured value is below a predetermined constant value, the nozzle A method for detecting nozzle clogging in an airless paint sprayer, characterized by detecting clogging of the nozzle d. Converting only ultrasonic waves within a frequency band of 20 kHz or higher, including a microphone placed near the nozzle of a spray gun of an airless paint sprayer, into a signal current. an amplifier for amplifying the signal current, and a signal generator for generating a nozzle clogging detection signal when the amplified signal current is below a certain value, are connected to the sonic wave detection device in sequence. Nozzle clogging detection device 3 for an airless paint sprayer, characterized in that
A nozzle clogging detection device for an airless paint sprayer according to claim 2, characterized in that the device is a ceramic microphone that detects sound waves in a specific frequency range within an ultrasonic band of kHz or higher.