Air Bubble Detection Sensor

Abstract

To provide an air bubble detection sensor which is free of variation in reception sensitivity and does not require adjusting a resonance frequency during manufacturing, and with which it is possible to reduce manufacturing cost.SOLUTION: An air bubble detection sensor according to the present invention is constituted by: a first and a second piezoelectric vibration plate in which a piezoelectric element is pasted to one surface of a metal sheet and the metal sheet is located so as to face each other across a prescribed interval; a fluid passage which is formed between the first and second piezoelectric vibration plates; a pulse generator for applying a single pulse to the piezoelectric element of the first piezoelectric vibration plate and causing the first piezoelectric vibration plate to generate a sound wave; a signal detector for detecting a signal having been generated to the piezoelectric element of the second piezoelectric vibration plate upon receiving the sound wave having propagated through the fluid; and a determiner that determines the percentage of air bubbles contained in the fluid, on the basis of the strength of the signal detected by the signal detector.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an air bubble detection sensor that detects the proportion of air bubbles contained in a liquid flowing inside a pipe, and more particularly to an air bubble detection sensor that is suitable for checking the remaining amount of ink in an inkjet printer. [Background technology]

[0002] In inkjet printers (hereafter referred to as "IJP") that use cartridges to supply ink, the amount of ink remaining can be checked by the user visually through a window in the cartridge or by a remaining amount detection sensor built into the cartridge. In recent years, the amount of ink remaining is estimated from the operating time of the ink supply pump.

[0003] Among the above-mentioned methods, visual inspection requires the operator to carry out the inspection, which hinders labor saving, while providing a sensor inside the cartridge increases costs. Also, the method of estimating the remaining amount of ink from the operation time of the pump generates errors due to variations in the amount of ink replenished.

[0004] One way to solve these problems would be to attach a sensor to the tube (piping) connecting the cartridge and the print head and check the remaining ink level by detecting when the proportion of air bubbles in the ink increases.

[0005] The inventors previously proposed an air bubble detection sensor that detects the amount of air bubbles in a liquid by attaching an ultrasonic sensor to the outside of a stainless steel pipe (SUS pipe) and utilizing the fact that the signal received by the sensor differs depending on whether liquid or air is present in the pipe (see Patent Document 1).

[0006] The air bubble detection sensor described in Patent Document 1 has a simple structure yet has sufficient sensitivity, making it suitable as a sensor for checking the remaining amount of ink. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2018-36123 A Summary of the Invention [Problem to be solved by the invention]

[0008] On the other hand, the sensor described in Patent Document 1 has a problem in that there is variation in the adhesion between the SUS tube and the ring-shaped piezoelectric element, resulting in differences in the output waveform even when the same waveform is input.

[0009] In addition, the sensor inputs a continuous wave that matches the resonant frequency, but since the resonant frequency depends on the arrangement and assembly state of the piezoelectric element, it is necessary to measure the resonant frequency each time it is attached to the SUS pipe, which increases manufacturing costs. Furthermore, a case is required to protect the electrodes of the piezoelectric element.

[0010] The present invention has been made in consideration of these conventional problems, and aims to provide an air bubble detection sensor which has little variation in receiving sensitivity, does not require adjustment of the resonant frequency during manufacturing, and enables reduction in manufacturing costs. [Means for solving the problem]

[0011] The air bubble detection sensor according to the present invention, which achieves the above object, comprises: A first piezoelectric diaphragm having a piezoelectric element attached to one surface of a thin metal plate, the first piezoelectric diaphragm functioning as a transmitter of sound waves; A second piezoelectric diaphragm having a piezoelectric element attached to one surface of a thin metal plate, the thin metal plate being disposed so as to face the thin metal plate of the first piezoelectric diaphragm at a predetermined distance, and functioning as a receiver of sound waves; a liquid flow path formed between the first and second piezoelectric diaphragms; a pulse generator that applies a single pulse to a piezoelectric element of the first piezoelectric diaphragm to generate a sound wave in the first piezoelectric diaphragm; a signal detector that detects a signal generated in a piezoelectric element of the second piezoelectric diaphragm by receiving a sound wave that has propagated through the liquid; and a determiner that determines the proportion of air bubbles contained in the liquid based on the strength of the signal detected by the signal detector.

[0012] Here, it is preferable that the first and second piezoelectric vibration plates are arranged on both sides of an insulating first plate, and that an opening forming a liquid flow path is formed in a portion of the first plate adjacent to the piezoelectric element.

[0013] Also, second and third insulating plates are disposed in contact with the outer surfaces of the first and second piezoelectric diaphragms, It is preferable that the second and third plates each have an opening formed in a position adjacent to the piezoelectric element of the first and second piezoelectric vibration plates, and each have a hole formed therein communicating with the opening of the first plate, and that the respective holes and the opening of the first plate form a flow path for the liquid.

[0014] The pulse generator also generates a single square wave pulse; the signal detector extracts a reception signal of the piezoelectric element of the second piezoelectric diaphragm when a predetermined time has elapsed since the pulse generator outputted a pulse; It is preferable that the determiner determines the proportion of air bubbles contained in the liquid by comparing the intensity of the extracted signal with a predetermined threshold value.

[0015] It is also preferable that the liquid is ink supplied to a print head from an ink tank of an inkjet printer, and the determiner determines whether or not the ink contains a large proportion of air bubbles. Effect of the Invention

[0016] The air bubble detection sensor according to the present invention can realize an air bubble detection sensor that has sufficient sensitivity and little output variation despite its simple structure. Moreover, since the structure is made by simply stacking three thin metal plates that make up the transmitter and receiver, which also serve as a liquid flow path, it is possible to significantly reduce manufacturing costs. [Brief description of the drawings]

[0017] [Figure 1] 1 is a development view showing a configuration of an air bubble detection sensor according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the air bubble detection sensor. [Diagram 3] FIG. 2 is a block diagram showing the configuration of an electrical system of the air bubble detection sensor. [Figure 4] 10 is a diagram showing a pulse waveform of a pulse generator and a received waveform of a signal detector when the distance between two piezoelectric diaphragms is set to 1 mm in the air bubble detection sensor according to the embodiment. FIG. [Diagram 5] 13 is a diagram showing a pulse waveform of a pulse generator and a received waveform of a signal detector when the distance between two piezoelectric diaphragms is 3 mm in the air bubble detection sensor according to the embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An air bubble detection sensor according to an embodiment of the present invention will now be described with reference to the drawings.

[0019] <Air bubble detection sensor configuration and functions of each part> Fig. 1 is a development view of the air bubble detection sensor according to the present embodiment, Fig. 2 is a cross-sectional view of the same sensor, and Fig. 2(b) is an enlarged view of a circle B area in the cross-section of Fig. 2(a).

[0020] The air bubble detection sensor 1 employs a structure in which an insulating resin plate 2, in which a diamond-shaped opening 21 that serves as an ink flow path, is sandwiched between two piezoelectric diaphragms 3 and 4. The piezoelectric diaphragm 3 is a rectangular metal thin plate 31 with a thin-film circular piezoelectric element 32 attached to one side thereof, and has a structure similar to that of commercially available piezoelectric buzzers.

[0021] Like the piezoelectric diaphragm 3, the piezoelectric diaphragm 4 also has a thin-film circular piezoelectric element 42 attached to one surface of a rectangular metal thin plate 41.

[0022] The piezoelectric diaphragms 3 and 4 function as transmitters or receivers for sound waves. Of these, the piezoelectric diaphragm 3 functions as a transmitter of sound waves, and when a pulse voltage generated by the pulse generator 11 is applied to the piezoelectric element 32, the piezoelectric element expands or contracts, and accordingly the thin metal plate 31 to which the piezoelectric element 32 is bonded bends, and sound waves are emitted from the thin metal plate 31.

[0023] On the other hand, the piezoelectric diaphragm 4 functions as a receiver of sound waves, and when sound waves are incident on the thin metal plate 41, the piezoelectric element 42 attached thereto is distorted, and an electric signal is output from the piezoelectric element 42. The signal detector 14 detects the intensity of the sound waves received by the piezoelectric diaphragm 4 based on the electric signal output from the piezoelectric element 42.

[0024] As will be described later, the propagation of the sound waves radiated from the piezoelectric diaphragm 3 varies greatly depending on the characteristics of the ink interposed between the piezoelectric diaphragm 3 and the piezoelectric diaphragm 4. When the space between the piezoelectric diaphragms 3 and 4 is filled with ink, the attenuation of the sound waves is small, and the degree of attenuation increases as the proportion of air bubbles, i.e., air, contained in the ink increases.

[0025] Therefore, if the relationship between the proportion of air bubbles contained in the ink and the output signal of the piezoelectric element 42 is investigated through experiments, the amount of air bubbles contained in the ink can be estimated from the strength of the output signal of the piezoelectric element 42.

[0026] The outside of the two piezoelectric vibration plates 3 and 4 is covered with insulating resin plates 5 and 6 which form part of the ink flow path, and circular openings 51 and 61 are formed in the central parts of the resin plates 5, 6 near the piezoelectric elements 32 and 42 so as not to interfere with the vibration of the piezoelectric vibration plates 3 and 4.

[0027] A hole is formed near the opening 51 of the resin plate 5, and the tip of the joint 7 is inserted into the hole and glued. The joint 7 constitutes an ink flow path, and a hole 71 is formed in the center, with one tip of the hole 71 communicating with the opening 21 formed in the center of the resin plate 2. The other tip of the hole 71 is connected to the IJP piping (not shown).

[0028] A hole is also formed in the resin plate 6 near the opening 61 at a position not facing the joint 7, and the tip of the joint 8 is inserted into the hole and adhered. The joint 8 forms an ink flow path in the same manner as the joint 7, and a hole 81 is formed in the center, with one tip of the hole 81 communicating with the opening 21 formed in the center of the resin plate 2. The other tip of the hole 81 is connected to the piping (not shown) of the IJP.

[0029] The resin plates 2, 5 and 6 and the piezoelectric diaphragms 3 and 4 are integrally secured to each other by a plurality of screws 9 from both the top and bottom, allowing the sensor to be easily assembled.

[0030] As described above, hole 71 of joint 7, hole 81 of joint 8, and opening 21 of resin plate 2 form an ink flow path, and ink pumped up from an ink tank using a pump (not shown) is transported through hole 71 of joint 7 to opening 21 of resin plate 2, as shown by the arrow in FIG. 2(a), and then passed through hole 81 of joint 8 to be supplied to a print head (not shown).

[0031] Although not shown in the figure, an electrode is formed on the outer surface of the thin-film piezoelectric element 32, and a lead wire 33 is connected to the electrode by soldering, as shown in Fig. 2(b). Similarly, an electrode is formed on the outer surface of the thin-film piezoelectric element 42, and a lead wire 43 is connected to the electrode by soldering.

[0032] Small holes are formed in two places on the periphery of each of the three resin plates 2, 5, and 6 so as to penetrate the plate, and metal pins 34 and 44 are inserted into the small holes. These pins 34 and 44 are used to ground the piezoelectric elements 32 and 42.

[0033] That is, the thin metal plate 31 to which the piezoelectric element 32 is attached also serves as an electrode, and is grounded via the pin 34. Similarly, the thin metal plate 41 to which the piezoelectric element 42 is attached is grounded via the pin 44.

[0034] As described above, in this embodiment, the piezoelectric diaphragm 3 is used as a sound wave transmitter, and the piezoelectric diaphragm 4 is used as a sound wave receiver. Then, the sound waves passing through the ink between the piezoelectric diaphragms 3 and 4 are converted into an electric signal by the piezoelectric element 42 of the piezoelectric diaphragm 4, and the proportion of air bubbles contained in the ink is estimated based on the value of the electric signal.

[0035] The strength of the sound waves propagating through the ink varies greatly depending on the amount of air bubbles contained in the ink: when there are no air bubbles, the sound waves are at their maximum, and the greater the proportion of air bubbles contained in the ink, the more attenuated the sound waves become. Therefore, by comparing the value of the signal generated by the piezoelectric element 42 with a predetermined threshold value, the proportion of air bubbles contained in the ink can be determined.

[0036] In this embodiment, the insulating resin plates 2, 5, and 6 are made of synthetic resin, but they do not necessarily have to be made of synthetic resin, and other materials may be used as long as they have excellent insulating properties and workability.

[0037] 3 shows the configuration of the electrical system of the air bubble detection sensor 1. In this embodiment, unlike conventional air bubble detection sensors, a single square wave pulse is used as the drive signal for the transmitter (piezoelectric diaphragm 3), and the sound wave generated by this pulse is received by the receiver (piezoelectric diaphragm 4), making the configuration of the electrical system extremely simple.

[0038] More specifically, a single rectangular wave pulse generated by pulse generator 11 is amplified by amplifier 12, then input to piezoelectric element 32 and converted to sound wave A by piezoelectric diaphragm 3. Sound wave A propagated through the ink is then converted to an electrical signal by piezoelectric element 42 of piezoelectric diaphragm 4, amplified by amplifier 13, and input to signal detector 14.

[0039] As will be described later, the signal detector 14 extracts the output of the piezoelectric element 42 a certain time after a pulse is generated based on a timing signal from the pulse generator 11, and smoothes the signal to produce an output signal.

[0040] The strength of the signal detected by the signal detector 14 is compared with a predetermined threshold value in a determiner 15. If the strength of the signal is greater than the threshold value, it is determined that the proportion of air bubbles in the ink is small, and if the strength of the signal is less than the threshold value, it is determined that the proportion of air bubbles in the ink is large.

[0041] If the determiner 15 determines that the ink contains a large number of air bubbles, it notifies the user of the ink tank by sound or light that the ink in the ink tank is low and filled with air bubbles, for example by making a beep sound or blinking an LED at regular intervals.

[0042] <Explanation of measurement results> Next, with reference to Figures 4 and 5, the results of measuring the amount of air bubbles in water using the air bubble detection sensor 1 shown in Figures 1 and 2 will be described. Figure 4 is a diagram showing the pulse waveform of pulse generator 11 and the received waveform of signal detector 14 when the gap between piezoelectric diaphragms 3 and 4 is 1 mm, and Figure 5 is a diagram showing the pulse waveform of pulse generator 11 and the received waveform of signal detector 14 when the gap between piezoelectric diaphragms 3 and 4 is 3 mm.

[0043] In this embodiment, the piezoelectric element is a PZT (product number C-6) manufactured by Fuji Ceramics with a diameter of 9 mm and a thickness of 0.35 mm, the thin metal plate is a thin SUS steel plate with a length of 43 mm, a width of 26 mm and a thickness of 0.05 mm, and the insulating resin plates 2, 5 and 6 are polyphenylene sulfide plates with a length of 43 mm, a width of 26 mm and a thickness of 3.0 mm.

[0044] In the present embodiment, the pulse generator 11 and the signal detector 14 are realized using an FPGA (Field-Programmable Gate Array), which is a type of integrated circuit.

[0045] In the air bubble detection sensor in which the distance between the piezoelectric vibration plates 3 and 4 was set to 1 mm, when a single rectangular wave pulse with a pulse width of 1 μs and a voltage of 10 volts as shown in FIG. 4(a) was applied to the piezoelectric element 32, the signal shown in FIG. 4(c) was obtained in the piezoelectric element 42.

[0046] The window W1 shown in FIG. 4(b) indicates the period during which a signal to be compared with a threshold is extracted from the received waveform shown in FIG. 4(c), and the window W1 is set at a time T1 after the falling edge of a single rectangular wave pulse.

[0047] The received waveform in Figure 4(c) shows the waveform when the space between the piezoelectric diaphragms 3 and 4 is filled with water or air, and when the window W1 is set, a strong received signal is obtained when the space between the piezoelectric diaphragms 3 and 4 is filled with water. In contrast, when the space between the piezoelectric diaphragms 3 and 4 is filled with air, the output signal shows a value close to zero.

[0048] The state in which the space between the piezoelectric diaphragms 3 and 4 is filled with air is characteristically the same as the state in which the ink flow path is filled with air bubbles. Therefore, when the value of the signal extracted using the window W1 falls below the threshold, it can be determined that the ink in the ink tank is nearly empty.

[0049] The waveform of the output signal shown in Fig. 5(c) also shows the same tendency as the waveform shown in Fig. 4(c). The position of window W2 shown in Fig. 5(b) is slightly shifted backward compared to the position of window W1 shown in Fig. 4(b) (time T2 after the falling edge of the square wave pulse). This time delay is caused by the difference in the distance between piezoelectric diaphragms 3 and 4 (1 mm and 3 mm).

[0050] Comparing the output values ​​of the windows W1 and W2 shown in Figure 4(b) and Figure 5(b), the strength of the output signal clearly differs depending on whether water or air is present between the piezoelectric diaphragms 3 and 4. Therefore, by setting an appropriate value as the threshold, it is possible to reliably determine whether the space between the piezoelectric diaphragms is filled with air bubbles.

[0051] Note that the graphs in Figures 4 and 5 show the measurement results when the flow channel was filled with water, but since the physical properties of ink are similar to those of water, it is safe to assume that the results obtained will be similar to those when the flow channel is filled with ink.

[0052] In addition, the state in which the inside of the flow channel is filled with bubbles has almost no difference in physical properties from the state in which the inside of the flow channel is filled with air, so the inside of the flow channel may be considered to be filled with bubbles.

[0053] As described above, by using the air bubble detection sensor of this embodiment, it is possible to reliably detect whether or not the ink flow path is filled with air bubbles. Therefore, by installing the air bubble detection sensor of this embodiment midway through the ink piping of the IJP, it is possible to reliably notify the user that there is little ink remaining in the ink tank.

[0054] In addition, the air bubble detection sensor according to this embodiment is fabricated by stacking two piezoelectric vibration plates and three resin plates and then fastening them from both sides with screws, making the structure very simple and easy to manufacture.

[0055] Furthermore, the air bubble detection sensor according to this embodiment can be produced inexpensively using commercially available piezoelectric buzzer components, and further, since the ink flow path is formed within the resin plate, no special components for the flow path are required, making it more cost-effective than conventional sensors. [Explanation of symbols]

[0056] 1 Air bubble detection sensor 2, 5, 6 Resin plate 3, 4 Piezoelectric diaphragm 7, 8 Joint 9. Vis 11 Pulse generator 12, 13 Amplifier 14 Signal Detector 15 Judgment device 21, 51, 61 Openings 31, 41 Metal thin plate 32, 42 Piezoelectric element 33, 43 lead wire 34, 44 pin 71, 81 holes

Claims

1. A first piezoelectric diaphragm having a piezoelectric element attached to one surface of a thin metal plate, the first piezoelectric diaphragm functioning as a transmitter of sound waves; A second piezoelectric diaphragm having a piezoelectric element attached to one surface of a thin metal plate, the thin metal plate being disposed so as to face the thin metal plate of the first piezoelectric diaphragm at a predetermined distance, and functioning as a receiver of sound waves; a liquid flow path formed between the first and second piezoelectric diaphragms; a pulse generator that applies a single pulse to a piezoelectric element of the first piezoelectric diaphragm to generate a sound wave in the first piezoelectric diaphragm; a signal detector that detects a signal generated in a piezoelectric element of the second piezoelectric diaphragm by receiving a sound wave that has propagated through the liquid; and a determiner for determining a proportion of air bubbles contained in the liquid based on the intensity of the signal detected by the signal detector.

2. 2. The air bubble detection sensor according to claim 1, wherein the first and second piezoelectric vibration plates are arranged on both sides of an insulating first plate, and an opening forming a liquid flow path is formed in a portion of the first plate adjacent to the piezoelectric element.

3. second and third insulating plates are disposed in contact with outer surfaces of the first and second piezoelectric diaphragms; The second and third plates include: an opening is formed in each of the first and second piezoelectric diaphragms at a position adjacent to the piezoelectric element; 3. The air bubble detection sensor according to claim 2, further comprising holes each communicating with an opening of said first plate, each hole and the opening of said first plate forming a flow path for said liquid.

4. The pulse generator generates a single square wave pulse; the signal detector extracts a reception signal of the piezoelectric element of the second piezoelectric diaphragm when a predetermined time has elapsed since the pulse generator outputted a pulse; 4. The air bubble detection sensor according to claim 1, wherein the determiner determines a proportion of air bubbles contained in the liquid by comparing the intensity of the extracted signal with a predetermined threshold value.

5. the liquid is ink supplied to a print head from an ink tank of an inkjet printer; 5. The air bubble detection sensor according to claim 1, wherein the determiner determines whether or not a proportion of air bubbles contained in the ink is high.

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