JP6360529B2 - Bubble detection sensor - Google Patents

Description

  The present invention relates to a bubble detection sensor that detects bubbles contained in a liquid flowing in a pipe, and more particularly to a bubble detection sensor suitable for confirming the remaining amount of ink in an inkjet printer.

  In an ink jet printer that supplies ink using a cartridge, the amount of ink remaining can be confirmed visually by a user through a window provided in the cartridge, or from a remaining amount detection sensor incorporated in the cartridge, or from the cartridge. This is done by changing the pressure of the pump for suction.

  Of the above confirmation methods, visual inspection requires an operator to perform, thus hindering labor savings. On the other hand, if a sensor or pressure sensor is provided in the cartridge, it causes a cost increase. .

  As a means to solve these problems, a sensor is attached to a tube (piping) connecting the cartridge and the printer head, and when the bubbles contained in the ink increase, the remaining amount of ink is confirmed by detecting it. It is possible.

  Any of electricity, light, and sound is used as means for detecting bubbles contained in the liquid flowing in the tube.

  In the detection by electricity, the wiring is wound around the tube, and the difference in inductance due to the difference in permeability between ink (liquid) and air in the tube is detected, but the threshold value needs to be adjusted according to the permeability of the ink material. There is.

  Although detection by light is simple, it is necessary to adjust the threshold value in accordance with the color and refractive index of the ink material as in the case of electricity.

  On the other hand, detection by sound (vibration) is easy to adjust the threshold because the difference in acoustic impedance between the ink material and air (bubbles) is as large as 3750 times (ink material 1.5 Mrayl, air 0.0004 Mrayl). Furthermore, even if the type of ink material changes, there is no significant difference in acoustic impedance, so it is suitable as a method for detecting air and liquid.

JP 2009-229413 A

  Patent Document 1 discloses a sensor that detects the presence of a liquid flowing in a tube using ultrasonic waves. Specifically, an ultrasonic sensor is attached to the outside of a stainless steel pipe (SUS pipe), and the difference between signals received by the sensor depends on whether liquid or air is present in the pipe. The presence or absence of air is detected.

  The sensor described in Patent Document 1 has a simple structure and is excellent in maintainability because it is only necessary to attach a SUS tube to a tube for transferring ink. On the other hand, since the signal that can be detected by the sensor is weak, the detection error is large, and it is necessary to amplify the signal using a high-sensitivity amplifier.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a bubble detection sensor having a simple structure using ultrasonic waves as detection means at a low price.

In order to achieve the above object, a bubble detection sensor according to the present invention includes:
A metal pipe attached in the middle of a pipe that conveys liquid;
A first piezoelectric element attached to the outer periphery of the metal tube and generating ultrasonic waves;
A second piezoelectric element that is attached to the outer periphery of the metal tube and receives ultrasonic vibrations propagating through the metal tube and converts it into an electrical signal;
Drive means for generating a drive signal for the first piezoelectric element;
And determining means for determining whether or not bubbles are included in the metal tube based on a reception signal of the second piezoelectric element.

  Here, it is preferable to use a signal in which a rectangular wave is repeated at a constant interval as the drive signal.

  The reception signal of the second piezoelectric element is transmitted to the determination means via an amplification means, and the amplification means extracts a frequency component of a predetermined band from the reception signal of the second piezoelectric element. And an amplifier that amplifies the output signal of the bandpass filter.

  The determining means determines that the metal tube is filled with bubbles when the output value of the amplifying means is greater than or equal to a predetermined threshold, and the output value of the amplifying means is less than a predetermined threshold. In this case, it is determined that the metal tube is filled with a liquid.

  In addition, a cylindrical pipe is used as the metal tube, and ring-shaped piezoelectric elements having an inner diameter substantially equal to the outer diameter of the metal tube are used as the first and second piezoelectric elements, and the first and second piezoelectric elements are used. It is preferable to insert the metal tube into the hollow portion of the piezoelectric element and fix it with an adhesive.

  The length of the metal tube is preferably set to λ × (2n−1) / 2 (n is a natural number) where λ is the wavelength at the resonance frequency in the radial direction of the metal tube.

  Furthermore, it is preferable that the first and second piezoelectric elements have the same size, and the interval between the first and second piezoelectric elements is set to λ × m / 2 (m is a natural number).

  According to the present invention, it is possible to realize a bubble detection sensor having a sufficient sensitivity while having a simple structure at a low price.

It is a block diagram which shows the whole structure of the bubble detection sensor which concerns on Embodiment 1 of this invention. It is a perspective view which shows the external appearance of the sensor main body of the bubble detection sensor of FIG. It is a figure explaining the dimension of the sensor main body. It is a time chart which shows the drive signal (a) of a transmitter, and the received signal (b) of a receiver. It is a graph which shows the frequency characteristic of the drive signal of a transmitter, and the receiving signal of a receiver when a continuous rectangular wave is applied to a transmitter. It is a figure explaining the relationship between the structure of a sensor main body in Embodiment 2 of this invention, and a standing wave.

  Hereinafter, a bubble detection sensor according to an embodiment of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 shows the overall configuration of the bubble detection sensor according to Embodiment 1 of the present invention. In the following description, it is assumed that the bubble detection sensor is used as a means for confirming the remaining amount of ink in the ink jet printer.

  The bubble detection sensor 1 according to the present embodiment supplies a drive signal to the sensor main body 3 disposed in the middle of the tube 2 for transferring ink and the sensor main body 3 and processes a reception signal from the sensor main body 3. The signal processing circuit 4 warns when the remaining amount of ink is small and a lot of bubbles are included.

<Configuration and function of sensor body>
First, the configuration and function of the sensor body 3 will be described. The sensor body 3 includes a metal tube 31 attached between the two divided tubes 2 and two ring-shaped piezoelectric elements 32a and 32b attached to the outer peripheral surface of the metal tube 31. .

  The two ring-shaped piezoelectric elements 32a and 32b are equal in size, and the first piezoelectric element 32a is a vibrator that generates an ultrasonic wave by a drive signal supplied from the signal processing circuit 4, and is hereinafter referred to as a transmitter 32a. . On the other hand, the second piezoelectric element 32b is a vibrator that receives the ultrasonic vibration output from the transmitter 32a and propagates through the metal tube 31 and converts it into an electrical signal, and is hereinafter referred to as a receiver 32b.

  Before describing the sensor body 3 in detail, the principle of bubble detection will be described. The bubble detection sensor 1 according to the present invention detects the presence of bubbles by utilizing a phenomenon in which the characteristics of sound waves propagating through the metal tube 31 change depending on the presence or absence of liquid (ink in the present embodiment) flowing through the tube. When the remaining amount of liquid decreases and the amount of bubbles increases, it can be detected and notified to the user.

  Specifically, when the metal tube 31 filled with the liquid functions as a resonator with respect to the ultrasonic vibration sent from the transmitter 32a, the metal tube 31 is filled with bubbles that become an acoustic load. Since the resonance frequency of the metal tube 31 is shifted, the value of the reception signal of the receiver 32b changes. Therefore, it is possible to detect whether or not the amount of bubbles has increased by comparing the voltage values of the signals received by the receiver 32b.

  In the present embodiment, in order to increase the value of the signal received by the receiver 32b as much as possible, a signal (hereinafter referred to as “continuous rectangular wave”) in which a rectangular wave is repeated at a constant interval is used as a driving signal for the transmitter 32a. Furthermore, the mounting positions of the transmitter 32a and the receiver 32b are devised. Hereinafter, with reference to FIG. 2 and FIG. 3, the ultrasonic vibration propagated to the metal tube 31 will be described.

  FIG. 2 shows the appearance of the sensor body 3, and when a continuous rectangular wave drive signal is applied between a pair of electrodes 33 formed on both sides of a ring-shaped transmitter 32a, the transmitter 32a is radially moved as indicated by an arrow. To generate ultrasonic vibration. The ultrasonic vibration propagates through the metal tube 31 to reach the receiver 32b, vibrates the receiver 32b in the direction indicated by the arrow, and generates a voltage between the pair of electrodes 34 of the receiver 32b.

  FIG. 3 shows specific dimensions and arrangements of the metal tube 31 and the two piezoelectric elements 32a and 32b used in the present embodiment. In the present embodiment, a cylindrical pipe made of stainless steel (SUS) is used as the metal pipe 31, and the pipe is inserted into the hollow portions of the ring-shaped piezoelectric elements 32a and 32b. The outer diameter of the pipe is 3 mm, the thickness is 0.3 mm, and the length is 30 mm. As the ring-shaped piezoelectric elements 32a and 32b, Fuji Ceramic piezoelectric elements having an outer diameter of 6 mm, an inner diameter of 3 mm, and a thickness of 2 mm were used.

  Then, as shown in FIG. 3, the transmitter 32 a and the receiver 32 b were fixed at a position 10 mm away from the end of the metal tube 31 using an adhesive (trade name “Able Bond” manufactured by Henkel Japan).

  About the space | interval of the transmitter 32a and the receiver 32b, the driving of the transmitter 32a was repeated changing each position, and it set to 6 mm from which the received signal of the receiver 32b became the maximum. Similarly, for the drive signal applied to the transmitter 32a, a continuous rectangular wave having a repetition frequency of 315 kHz and a voltage of 1 V that changes the repetition frequency and maximizes the reception signal of the receiver 32b is used.

  FIG. 4A shows waveforms obtained by measuring the drive signal applied to the transmitter 32a and FIG. 4B measuring the received signal converted into an electrical signal by the receiver 32b with an oscilloscope. In FIG. 4B, the waveform indicated by the alternate long and short dash line is the waveform when the inside of the metal tube 31 is filled with air, and the waveform indicated by the solid line is the waveform when the inside of the metal tube 31 is filled with water. is there.

  Comparing the waveforms shown in FIGS. 4A and 4B, the received signal waveform is 45 degrees out of phase with the drive signal waveform. This is because the distance between the transmitter 32a and the receiver 32b is 6 mm, and it takes about 1 μS for the ultrasonic vibration to propagate through the metal tube 31 and reach the receiver 32b.

  There is almost no change in phase between when the metal tube 31 is filled with water and when it is filled with air, but the intensity of the received signal of the receiver 32b is changed when the water in the metal tube 31 is changed to air. About 1 / 2.6.

  FIG. 5 shows frequency characteristics of the drive signal and the reception signal. In the figure, a solid line indicates a drive signal, a one-dot chain line indicates a reception signal when the metal tube is filled with air, and a broken line indicates a reception signal when the metal tube is filled with water.

  From the figure, it can be confirmed that the dynamic range of each signal serving as an index of detection sensitivity is wide. It can also be seen that when the metal tube is filled with water, the frequency component of 700 kHz to 800 kHz is reduced by about 15 dB with respect to the reference resonance frequency.

  This means that the resonance energy of the metal tube when the inside of the metal tube is filled with air is dissipated when water enters. From this fact, it is possible to determine whether the metal tube is filled with water or air by comparing the values of the reception signals of the receiver 32b near 780 kHz.

<Configuration and function of signal processing circuit>
Next, the configuration and function of the signal processing circuit 4 of the bubble detection sensor 1 according to the present embodiment will be described with reference to the block diagram of FIG. 1 and the time chart of FIG. The signal processing circuit 4 includes a drive unit 41, an amplification unit 42, a control unit 43, a determination unit 44, and a warning unit 45.

  As indicated by the thin line arrows, the control unit 43 controls operations of the drive unit 41, the amplification unit 42, the determination unit 44, and the warning unit 45. The control unit 43 and the determination unit 44 are realized by a microprocessor, and a program for realizing these functions is stored in the memory.

  The drive unit 41 corresponds to the drive means described in the claims. Similarly, the amplification unit 42 corresponds to an amplification unit, and the determination unit 44 corresponds to a determination unit.

  The drive unit 41 generates a drive signal for the transmitter 32a, and includes a simple digital circuit such as a comparator. As described above, in this embodiment, a continuous rectangular wave is used as the drive signal (see FIG. 4A). Specifically, a continuous rectangular wave drive signal having a frequency of 315 kHz and a voltage of 1 V is applied between the pair of electrodes 33 of the transmitter 32a.

  The amplifying unit 42 amplifies the signal received by the receiver 32b and outputs the amplified signal to the determining unit 44. The amplifying unit 42 includes a band pass filter and an amplifier. When the received signal of the receiver 32b is passed through a narrow band-pass filter having a center frequency of 780 kHz, the output voltage value is different depending on whether the metal tube 31 is filled with ink or air. It changes a lot.

  The reception signal amplified by the amplifying unit 42 and from which a specific frequency component has been extracted is determined by the determining unit 44 in which a threshold is set in advance. If the voltage value of the received signal is smaller than the threshold value, it is determined that the metal tube 31 is filled with ink, and no signal is output to the warning unit 45. On the other hand, when the voltage value of the received signal is equal to or greater than the threshold value, it is determined that the inside of the metal tube 31 is filled with bubbles, and a signal is output to the warning unit 45.

  The warning unit 45 has a built-in speaker and LED, and the warning unit 45 that has received a signal from the determination unit 44 uses voice and light to fill the metal tube with bubbles, that is, there is little ink remaining. Let the user know.

  A user who knows that there is little ink remaining from the warning of the warning unit 45 fills the ink tank with ink or replaces the cartridge to prevent printing interruption or fading.

  Note that the threshold value in the determination unit 44 is set in consideration of the amount of bubbles contained in the ink. For example, the threshold value may be set when the ink flowing in the metal tube runs out and most of the ink becomes air.

  As described above, the bubble detection sensor according to the present embodiment has a simple structure and sufficient sensitivity, and can easily check the remaining amount of ink transferred from the ink tank to the ink head. Therefore, the maintainability of the ink jet printer can be greatly improved.

(Embodiment 2)
In the first embodiment, the interval between the transmitter 32a and the receiver 32b is set to a value that maximizes the received signal of the receiver 32b through experiments, but the length of the metal tube 31 is not particularly limited.

  On the other hand, in the present embodiment, the standing wave is generated in the metal tube 31, and the two piezoelectric elements 32a and 32b are installed at the antinodes of the standing wave, so that the maximum received signal of the receiver 32b can be obtained. We are trying to make it. FIG. 6 shows how the standing wave SW is generated by the ultrasonic vibration propagating through the metal tube 31.

  As described above, the amplitude of the ultrasonic wave generated by the transmitter 32a and the value of the reception signal generated by the receiver 23b are weak. As shown in FIG. 6, when the standing wave SW is generated in the metal tube 31 and the transmitter 32a and the receiver 32b are installed at the antinodes of the standing wave SW, the respective amplitudes become maximum. As a result, the value of the received signal of the receiver 32b is maximized with respect to the drive signal of the transmitter 32a.

  If the length L of the metal tube is set to L = λ × (2n−1) / 2 (n is a natural number) with respect to the wavelength λ at the resonance frequency in the radial direction of the metal tube, it depends on the length of the metal tube. A standing wave with no phase shift is generated. On the other hand, if the distance W between the transmitter and the receiver is W = λ × m / 2 (m is a natural number), the value of the received signal of the piezoelectric element is maximized.

The wavelength λ is obtained by the following formula.
Wavelength λ = (Sound velocity of ultrasonic wave propagating through metal tube) / (Resonance frequency in the radial direction of metal tube)

  More specifically, FIG. 6A shows a state where L = λ and W = λ / 2. Similarly, FIG. 6B shows a state where L = 3 / 2λ and W = λ / 2, FIG. 6C shows a state where L = 2λ and W = λ / 2, and FIG. The states of L = 5 / 2λ and W = 3 / 2λ are shown, respectively. By realizing any one of the states in FIGS. 6A to 6D, it is possible to increase the sensitivity of the sensor and improve the accuracy of determining the presence or absence of bubbles.

  In each of the above-described embodiments, the bubble detection sensor according to the present invention is used to check the remaining amount of ink in an inkjet printer, but the application of the sensor is not limited to this. The bubble detection sensor according to the present invention is also effective as means for detecting the remaining amounts of various liquids such as alcohol and chemicals.

DESCRIPTION OF SYMBOLS 1 Bubble detection sensor 2 Tube 3 Sensor main body 4 Signal processing circuit 31 Metal pipe 32a Transmitter (piezoelectric element)
32b Receiver (piezoelectric element)
33, 34 Electrode 41 Drive unit 42 Amplification unit 43 Control unit 44 Judgment unit 45 Warning unit

Claims (7)

A metal pipe attached in the middle of a pipe that conveys liquid;
A first piezoelectric element attached to the outer periphery of the metal tube and generating ultrasonic waves;
A second piezoelectric element that is attached to the outer periphery of the metal tube and receives ultrasonic vibrations propagating through the metal tube and converts it into an electrical signal;
Drive means for generating a drive signal for the first piezoelectric element;
A bubble detection sensor comprising: a determination unit that determines whether or not a bubble is included in the metal tube based on a reception signal of the second piezoelectric element.   The bubble detection sensor according to claim 1, wherein a signal in which a rectangular wave is repeated at a constant interval is used as a drive signal of the drive unit. A reception signal of the second piezoelectric element is transmitted to the determination unit via an amplification unit,
The amplifying unit includes a band-pass filter that extracts a frequency component of a predetermined band from the reception signal of the second piezoelectric element, and an amplifier that amplifies the output signal of the band-pass filter. The bubble detection sensor described in 1.   The determining means determines that the metal tube is filled with bubbles when the output value of the amplifying means is greater than or equal to a predetermined threshold, and the output value of the amplifying means is less than a predetermined threshold. 4. The bubble detection sensor according to claim 1, wherein the bubble detection sensor determines that the metal tube is filled with a liquid. A cylindrical pipe is used as the metal tube, and a ring-shaped piezoelectric element having an inner diameter substantially equal to the outer diameter of the metal tube is used as the first and second piezoelectric elements,
The bubble detection sensor according to any one of claims 1 to 4, wherein the metal tube is inserted into a hollow portion of the first and second piezoelectric elements and fixed with an adhesive.   6. The length of the metal tube is set to λ × (2n−1) / 2 (n is a natural number), where λ is a wavelength at a resonance frequency in a radial direction of the metal tube. The bubble detection sensor according to any one of the above.   The first and second piezoelectric elements have the same size, and an interval between the first and second piezoelectric elements is set to λ × m / 2 (m is a natural number). The bubble detection sensor described.

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