JP6729141B2 - Liquid level position detector - Google Patents

Description

The present invention relates to a liquid surface position detection device. The present invention particularly relates to a liquid surface position detection device that detects the position of the liquid surface of a liquid in a tank by using ultrasonic waves.

As a liquid surface position detecting device, an ultrasonic wave propagating body is placed in a tank, and the liquid surface is made by utilizing the difference between the speed of the surface wave propagating in the liquid and the speed of the surface wave propagating in the gas. Devices for detecting position are known. As a liquid surface position detecting device using such ultrasonic waves, there is one disclosed in Patent Document 1, for example.

In the liquid level position detection device disclosed in Patent Document 1, ultrasonic waves made of metal are arranged in a tank so that the longitudinal direction of the ultrasonic wave propagates vertically, and ultrasonic vibrations are provided at the upper end of the ultrasonic wave propagater. Vibrate the child. The liquid surface position detection device disclosed in Patent Document 1 detects the surface wave propagating on the surface of the ultrasonic wave propagating body and measures the propagation period of the surface wave. In the liquid surface position detecting device disclosed in Patent Document 1, by utilizing the fact that the velocity of the surface wave propagating in the liquid contact portion becomes slower than the velocity of the surface wave propagating in the exposed portion exposed from the liquid, The liquid surface position is detected according to the propagation period of the surface wave.

Here, the velocity of the surface wave propagating through the ultrasonic wave propagating body is affected by the temperature of the ultrasonic wave propagating body itself. That is, the density of the ultrasonic wave propagating body changes due to the temperature of the ultrasonic wave propagating body itself, and the velocity of the surface wave propagating through the ultrasonic wave propagating body changes depending on the density of the ultrasonic wave propagating body. Therefore, it is possible to provide a temperature sensor that detects the temperature of the ultrasonic wave propagating body, but when the temperature sensor is provided, there is a problem that the manufacturing cost increases.

In order to solve this problem, the liquid surface position detection device disclosed in Patent Document 2 has been proposed. The liquid surface position detecting device disclosed in Patent Document 2 generates a surface wave propagating on the surface of the propagating body as the vibration of the propagating body and also an internal propagating wave propagating inside the propagating body. The speed at which the internal propagating wave propagates inside the propagating body is not affected by the length of contact of the propagating body with the liquid, but is affected only by the temperature of the propagating body. In the liquid surface position detection device disclosed in Patent Document 2, the speed at which the surface wave propagates on the surface of the propagating body is corrected by the speed at which the internal propagating wave propagates inside the propagating body. As a result, the liquid surface position detection device disclosed in Patent Document 2 does not need to include a temperature sensor, and can consider the influence of the temperature of the propagating body.

By the way, Patent Document 2 discloses that the propagating body is provided with an internal propagating wave reflection portion for reflecting the internal propagating wave. The present inventors have recognized that the detection accuracy of the internal propagating wave and the surface wave is improved by providing the internal propagating wave reflector at an appropriate position on the propagating body.

JP-A-4-86525 JP, 2016-125825, A

An object of the present invention is to provide a liquid surface position detecting device that can detect the position of the liquid surface with high accuracy by using ultrasonic waves without using a temperature sensor. Other objects of the present invention will become apparent to those skilled in the art by referring to the aspects and preferred embodiments illustrated below, and the accompanying drawings.

A first aspect according to the present invention is a vibration generating unit that vibrates a piezoelectric element by applying a voltage to the piezoelectric element,
A propagating body that propagates the vibration of the piezoelectric element,
A vibration detection unit that detects that the vibration is reflected by the reflection unit of the propagating body and is input to the piezoelectric element,
A position determining unit that determines the position of the liquid surface of the liquid in which the propagating body is immersed;
A liquid surface position detecting device comprising:
The propagating body propagates a surface wave in which the vibration propagates on a surface of the propagating body and an internal propagating wave in which the vibration propagates inside the propagating body,
The reflecting portion includes a surface wave reflecting portion and an internal propagating wave reflecting portion,
The position determining unit is immersed in the propagating body based on a surface wave propagation period, which is a period from when the vibration is generated to when the surface wave is reflected by the surface wave reflecting unit and is input to the piezoelectric element. Determining the position of the liquid surface of the liquid,
The position determining unit propagates the surface wave by an internal propagating wave propagation period which is a period from when the vibration is generated to when the internal propagating wave is reflected by the internal propagating wave reflecting unit and is input to the piezoelectric element. Correct the period,
The surface acoustic wave reflection portion is one of two end portions in the longitudinal direction of the propagating body, which is farther from the piezoelectric element.
The internal propagating wave reflector is formed at a position on the propagating body such that a period obtained by multiplying the internal propagating wave propagation period by n (n is an integer of 1 or more) does not overlap with the surface wave propagating period , The surface when the position of the liquid surface of the liquid in which the propagating body is immersed is highest in both the period in which the internal propagating wave propagation period is multiplied by n and the period in which the internal propagating wave propagation period is multiplied by n+1 as it not included between said surface wave propagation period when the position of the liquid surface of the liquid in which the propagating body and the wave propagation time is immersed lowest, Ru is formed at a position on the propagation member The present invention relates to a liquid level position detecting device.

By providing the internal propagating wave reflection part so that the period obtained by multiplying the internal propagating wave propagation period by n does not overlap with the surface wave propagating period, it is possible to prevent the reflected internal propagating wave from interfering with the surface wave. It is distinguished whether the generated internal propagating wave or surface wave is input to the piezoelectric element.

By forming the internal propagating wave reflector at the position on the propagating body so as to satisfy such a condition, the reflected internal propagating wave and the surface wave do not interfere with each other.

ここで、
ｖｓは、内部伝搬波の伝搬速度であり、
ｖｒは、気体内での表面波の伝搬速度であり、
ｖｌｒは、液体内での表面波の伝搬速度であり、
Ｌ１は、伝搬体における、圧電素子に近い側の端部から内部伝搬波反射部までの長さであり、
Ｌ２は、伝搬体の全長であり、
Ｌ３は、伝搬体における、圧電素子に近い側の端部から液体の液面の位置が最も高いときの液面の位置までの長さである。
In a third aspect according to the present invention, in the first aspect, the internal propagating wave reflection unit is configured to perform the following when the propagation velocity of the surface wave in the gas is higher than the propagating velocity of the surface wave in the liquid. While being formed at a position on the propagating body so as to satisfy the equation (1), the propagation speed of the surface wave in the gas is slower than the propagation speed of the surface wave in the liquid. May be formed at a position on the propagating body so as to satisfy the equation (2).

here,
vs is the propagation velocity of the internal propagating wave,
vr is the propagation velocity of the surface wave in the gas,
vlr is the propagation velocity of the surface wave in the liquid,
L1 is the length from the end of the propagating body closer to the piezoelectric element to the internal propagating wave reflection portion,
L2 is the total length of the propagator,
L3 is the length from the end of the propagating body on the side closer to the piezoelectric element to the position of the liquid surface when the position of the liquid surface is the highest.

By forming the internal propagating wave reflection portion in the propagating body within the range of L1 that satisfies the formula (1), the period of n times the internal propagating wave propagation period is the liquid surface of the liquid in which the propagating body is immersed. Does not overlap with the surface wave when the position of is within the detection range.

According to a fourth aspect of the present invention, in the third aspect, the amplitude of the internal propagating wave reflected by the internal propagating wave reflecting portion and input to the piezoelectric element at the time point of multiplying the internal propagating wave propagation period by n+1. Is smaller than the given amplitude,
The internal propagating wave reflection unit is configured to satisfy the following formula (3) instead of the formula (1) or the following formula (4) instead of the formula (2). It may be formed at the upper position.

When the amplitude of the internal propagating wave, which is reflected by the internal propagating wave reflector and is input to the piezoelectric element at the time when the internal propagating wave propagation period is multiplied by n+1, is smaller than a predetermined amplitude, Equation (3) or (4) is used. Even if the internal propagating wave reflector is formed in the propagating body within the range of L1 to be satisfied, the position of the liquid surface of the liquid in which the propagating body is immersed does not overlap with the surface wave when the liquid level is within the detection range.

In a fifth aspect according to the present invention, in the first to fourth aspects, the length from the end of the propagating body closer to the piezoelectric element to the internal propagating wave reflecting portion is the total length of the propagating body. N may be 1 when it is longer than half of

The internal propagating wave is attenuated and its amplitude becomes smaller as the number of times of reflection by the internal propagating wave reflecting section increases. That is, when n, which is the number of times the internal propagating wave is reflected by the internal propagating wave reflecting section, is 1, the amplitude of the internal propagating wave input to the piezoelectric element is the largest, and the detection by the vibration detecting section is easy.

It is a figure which shows the example of a structure of the liquid surface position detection apparatus which concerns on this invention. It is a figure which shows the relationship of the position of a liquid level, and a surface wave and an internal propagation wave. It is a flowchart figure which shows the example of operation|movement of the liquid level position detection apparatus shown by FIG. It is a figure explaining the position where an internal propagation wave reflection part is provided in a propagation object. It is a figure explaining the conditions for providing an internal propagation wave reflection part in an appropriate position on a propagation body. It is a figure explaining the conditions for providing an internal propagation wave reflection part in an appropriate position on a propagation body.

The preferred embodiments described below are used to facilitate an understanding of the present invention. Therefore, those skilled in the art should note that the present invention is not unduly limited by the embodiments described below.

<<1. Example of overall configuration>>
As shown in FIG. 1, the liquid surface position detection device 10 is a device that detects the position of the liquid surface 81 of the liquid 80 stored in the container 70. The container 70 is, for example, a fuel tank, and the liquid 80 is, for example, gasoline. With the use and refueling of gasoline, the position of the liquid surface 81 moves up and down. The container 70 is not limited to the fuel tank, and may be a general container as long as it can store the liquid 80. The liquid 80 is not limited to gasoline, and may be fuel such as alcohol or water, and any liquid may be used.

The liquid surface position detecting device 10 includes a propagating body 20, a piezoelectric element 31, a vibration generating unit 32, a vibration detecting unit 33, and a position determining unit 40. The propagating body 20, the piezoelectric element 31, the vibration generating unit 32, the vibration detecting unit 33, and the position determining unit 40 are housed inside a case 50. The case 50 is fixed to the container 70.

The propagating body 20 is made of a resin material. The resin material is, for example, polyphenylene sulfide (PPS). By using PPS as the material of the propagating body 20, ultrasonic waves (surface wave W2, internal propagating wave W1) can be satisfactorily propagated. It should be noted that the resin material is not limited to PPS and may be any other general resin as long as it can propagate ultrasonic waves.

The propagating body 20 has a vertically long rectangular prism shape. However, the shape of the propagating body 20 is not limited to a quadrangular prism, and may be any other shape as long as it has a vertically long pillar shape such as a cylinder or a triangular prism. Since the propagating body 20 has a vertically long shape, it can be immersed in the liquid 80.

The propagating body 20 is provided with a groove 21 cut out in the middle of the longitudinal direction. The groove 21 includes an internal propagating wave reflection portion 22 that reflects the internal propagating wave. Further, of the two end portions 24 and 25 of the propagating body 20, the end portion 24 on the side far from the piezoelectric element 31 reflects the surface wave. The end portion 24 of the propagating body 20 on the side far from the piezoelectric element 31 is also referred to as a surface wave reflecting portion 24, and the internal propagating wave reflecting portion 22 and the surface wave reflecting portion 24 are collectively referred to as a reflecting portion of the propagating body 20.

The piezoelectric element 31 has a surface on which the groove 21 is not provided from the end 25 on the side close to the piezoelectric element 31 to the end 24 on the side far from the piezoelectric element 31 (the surface itself and the surface of the propagator 20 from the surface). A part of the piezoelectric element 31 is arranged so as to protrude from the main surface 26, which is a region up to a predetermined depth shorter than the thickness). Further, the bottom surface of the piezoelectric element 31 is in close contact with the upper surface of the bottom of the case 50, and the end 25 of the propagating body 20 on the side closer to the piezoelectric element 31 is in close contact with the lower surface of the bottom of the case 50. As a result, the surface wave W2 and the internal propagating wave W1 can be generated in the propagating body 20, and the surface wave W2 and the internal propagating wave W1 can be detected.

When the piezoelectric element 31 vibrates, it vibrates the propagating body 20 through the bottom of the case 50 to generate a surface wave W2 on the main surface 26 of the propagating body 20 and to generate an internal propagating wave W1 inside the propagating body 20. generate. Further, the piezoelectric element 31 detects the surface wave W2 reflected by the end portion 24 of the propagating body 20 and the internal propagating wave W1 reflected by the internal propagating wave reflector 22 and converts them into a voltage. The surface wave W2 includes a Rayleigh wave (a surface wave propagating in a gas) and a leaky Rayleigh wave (a surface wave propagating in a liquid), and the internal propagating wave W1 includes a transverse wave. Further, in general, the internal propagation wave propagation speed, which is the speed at which the internal propagation wave W1 propagates through the propagating body 20, is faster than the surface wave propagation speed, which is the speed at which the surface wave W2 propagates through the propagating body 20. Alternatively, the piezoelectric element 31 may directly contact the propagating body 20. With such a structure, it is expected that the internal propagating wave W1 and the surface wave W2 can be transmitted to the propagating body 20 with a strong amplitude.

The vibration generator 32 is configured to vibrate the piezoelectric element 31 by applying a voltage to the piezoelectric element 31. For example, the vibration generation unit 32 applies a voltage to the piezoelectric element 31 according to the drive signal output by the position determination unit 40 in a predetermined cycle.

The vibration detection unit 33 generates a piezoelectric wave when the surface wave W2 or the internal propagation wave W1 is reflected by the internal propagation wave reflection unit 22 or the surface wave reflection unit 24 that is the reflection unit of the propagating body 20 and is input to the piezoelectric element 31. It is configured to detect the voltage output by the element 31. The vibration detection unit 33 may output a detection signal to the position determination unit 40 when detecting the voltage, for example. In addition, in the example shown in FIG. 1, the vibration generation unit 32 and the vibration detection unit 33 are configured as separate bodies, but the present invention is not limited to this, and the vibration generation unit 32 and the vibration detection unit 33 are configured as one body. May be.

The position determination unit 40 is configured by, for example, a microcomputer, and includes a processing unit 41 configured by a CPU (Central Processing Unit) and the like, a RAM (Random Access Memory), a ROM (Read Only Memory), and the like. And a storage unit 42 for storing the data. The position determination unit 40 determines the position of the liquid surface 81 of the liquid 80 in which the propagating body 20 is immersed, and a detailed description will be given later.

In the example shown in FIG. 1, the position determining unit 40 is provided inside the case 50, but the present invention is not limited to this, and the position determining unit 40 may be provided in an external device arranged outside the case 50. Good. Further, the position determination unit 40 may include at least one of the vibration generation unit 32 and the vibration detection unit 33.

<<2. Example of operation>>
An example of the operation of the liquid surface position detection device 10 will be described with reference to FIGS. 2 and 3. First, the basic principle of calculating the height of the liquid surface 81 will be described with reference to FIG. Explaining the outline, the height of the liquid surface 81 is obtained from the surface wave propagation period T2 of the surface wave W2 and the internal propagation wave propagation period T1 of the internal propagation wave W1. The details will be described below.

As a premise, the propagating body 20 has a different surface wave propagation velocity in a gas than in a liquid. Further, which of the surface wave propagation velocity in the gas and the surface wave propagation velocity in the liquid becomes faster depends on the material of the propagating body 20. FIG. 2 shows an example in which the propagating body 20 is made of a material whose surface wave propagation velocity in gas is higher than that in liquid.

On the upper side of FIG. 2, when the position of the liquid surface 81 is low, the internal propagating wave W1 and the surface wave W2-L propagated by the propagating body 20 due to the generation of vibration are reflected and input to the piezoelectric element 31. The situation is shown. Further, in the lower side of FIG. 2, in a situation where the position of the liquid surface 81 is high, the internal propagating wave W1 and the surface wave W2-H propagating by the propagating body 20 due to the generation of vibration are reflected and the piezoelectric element 31 is reflected. Is shown.

A time point t0 shown in FIG. 2 is a time point when the vibration W0 occurs, that is, a time point when the position determining unit 40 outputs the drive signal. As described above, when the vibration W0 is generated, the propagating body 20 propagates the internal propagating wave W1 and the surface wave W2. The time point t1 shown in FIG. 2 is a time point when the internal propagating wave W1 is reflected by the internal propagating wave reflecting portion 22 and is input to the piezoelectric element 31. The period T1 shown in FIG. 2 is the internal propagation wave propagation period T1 which is the period from time t0 to time t1.

A time point t2-L shown in FIG. 2 is a time point when the surface wave W2-L is reflected by the surface wave reflection portion 24 and is input to the piezoelectric element 31 in a situation where the position of the liquid surface 81 is low. Further, a time point t2-H shown in FIG. 2 is a time point when the surface wave W2-H is reflected by the surface wave reflection portion 24 and input to the piezoelectric element 31 in a situation where the position of the liquid surface 81 is high.

In the example shown in FIG. 2, since the surface wave propagation velocity in the gas is higher than the surface wave propagation velocity in the liquid, the time point t2-L is earlier than the time point t2-H. As a result, the surface wave propagation period T2-L, which is the period from time t0 to time t2-L, is shorter than the surface wave propagation period T2-H, which is the period from time t0 to time t2-H. Thus, in the example shown in FIG. 2, the lower the position of the liquid surface 81, the shorter the surface wave propagation period T2, and the higher the position of the liquid surface 81, the longer the surface wave propagation period T2. Utilizing this, the position determination unit 40 causes the processing unit 41 to calculate an arithmetic expression, a table, or the like stored in the storage unit 42 and indicating the relationship between the surface wave propagation period T2 and the position of the liquid surface 81. Alternatively, by referring to it, the position of the liquid surface 81 according to the surface wave propagation period T2 can be determined.

By the way, the internal propagating wave propagation velocity and the surface wave propagating velocity are affected by the temperature of the propagating body 20. That is, the density of the propagating body 20 changes due to the temperature of the propagating body 20, and the internal propagating wave propagation velocity and the surface wave propagating velocity change depending on the density and/or elastic modulus of the propagating body 20. Here, since the internal propagating wave W1 travels inside the propagating body 20, the internal propagating wave propagation velocity (internal propagating wave propagating period T1) is not affected by the length of the propagating body 20 immersed in the liquid 80, Only the temperature of the propagating body 20 is affected.

Therefore, the temperature of the propagating body 20 is obtained from the internal propagating wave propagation period T1 of the internal propagating wave W1 with reference to the temperature condition stored in the storage unit 42 of the position determining unit 40. The surface wave propagation period T2 of the surface wave W2 is corrected based on the temperature of the propagating body 20 using a correction method that takes into consideration a predetermined correction coefficient and the like. By the position determining unit 40 determining the position of the liquid surface 81 according to the corrected surface wave propagation period T2, it is possible to determine the position of the liquid surface 81 with high accuracy in consideration of the temperature of the propagating body 20. ..

Next, with reference to FIG. 3, a series of operations of the liquid surface position detection device 10 will be described. In step ST01, the vibration generator 32 generates the vibration W0. In step ST02, the position determination unit 40 determines whether or not the internal propagating wave W1 reflected by the piezoelectric element 31 is input. When the determination in step ST02 is YES, the flow proceeds to step ST03, and when the determination in step ST02 is NO, the flow proceeds to step ST01.

In step ST03, the position determination unit 40 acquires the internal propagation wave propagation period T1. In step ST04, the position determination unit 40 determines the temperature of the propagating body 20 based on the internal propagating wave propagation period T1. In step ST05, the position determination unit 40 determines whether or not the surface wave W2 reflected by the piezoelectric element 31 is input. When the determination in step ST05 is YES, the flow proceeds to step ST06, and when the determination in step ST05 is NO, the flow proceeds to step ST01.

In step ST06, the position determination unit 40 acquires the surface wave propagation period T2. In step ST07, the position determination unit 40 corrects the surface wave propagation period T2 based on the temperature of the propagating body 20 determined in step ST04. In step ST08, the position determination unit 40 determines the position of the liquid surface 81 according to the corrected surface wave propagation period T2. When the process of step ST08 is completed, the flow ends.

<<3. Position of internal propagating wave reflector>>
Hereinafter, in the propagating body 20, an appropriate position where the internal propagating wave reflecting portion 22 is provided will be described. First, as a premise, the reason why the internal propagating wave reflection portion 22 is provided in the propagating body 20 will be described.

As described above, the internal propagating wave W1 and the surface wave W2 propagating in the propagating body 20 are generated by the same vibration of the piezoelectric element 31, are reflected by the reflecting portion of the propagating body 20, and are input to the piezoelectric element 31, respectively. The piezoelectric element 31 outputs a voltage when the reflected internal propagation wave W1 or surface wave W2 is input. The vibration detector 33 detects the voltage output by the piezoelectric element 31 and outputs a detection signal to the position determiner 40.

Here, the vibration detection unit 33 and the position determination unit 40 cannot distinguish whether the vibration (wave) input to the piezoelectric element 31 is the reflected internal propagation wave W1 or the surface wave W2. Therefore, timing data including an expected period from the occurrence of vibration to the input of the reflected internal propagation wave W1 and surface wave W2 to the piezoelectric element 31 is stored in advance in, for example, the storage unit 42 of the position determination unit 40. ing. For example, the position determination unit 40 refers to the timing data, and based on the period from the occurrence of vibration to the input of the detection signal, which of the reflected internal propagation wave W1 or surface wave W2 is transmitted to the piezoelectric element 31. Determine whether you have entered.

By the way, when the reflected internal propagating wave W1 and the surface wave W2 interfere with each other, for example, it is possible to accurately determine which of the internal propagating wave W1 and the surface wave W2 reflected by the position determining section 40 is input to the piezoelectric element 31. Becomes difficult. Therefore, the propagating body 20 is provided with the internal propagating wave reflecting portion 22 so that the propagating length of the internal propagating wave W1 is different from the propagating length of the surface wave W2. As a result, by providing the internal propagating wave reflection part 22 at an appropriate position on the propagating body 20, the reflected internal propagating wave W1 and the surface wave W2 are prevented from interfering with each other, and the reflected internal propagating wave W1 is prevented. Alternatively, the position determining unit 40 can accurately determine which of the surface waves W2 is input to the piezoelectric element 31.

Next, with reference to FIG. 4, an appropriate position in the propagating body 20 where the internally propagating wave reflecting portion 22 is provided will be described. FIG. 4 schematically shows the propagating body 20, the piezoelectric element 31, and the liquid surface 81.

The length L1 shown in FIG. 4 indicates the length from the end portion 25 of the propagating body 20 on the side closer to the piezoelectric element 31 to the internal propagating wave reflecting portion 22 on the propagating body 20. The length L2 shown in FIG. 4 is the length from the end portion 25 of the propagating body 20 on the side closer to the piezoelectric element 31 to the end portion 24 of the propagating body 20 on the side farther from the piezoelectric element 31, that is, the propagating body 20. Shows the total length in the longitudinal direction of. The length L3 shown in FIG. 4 indicates the length from the end 25 of the propagating body 20 on the side closer to the piezoelectric element 31 to the position of the liquid surface 81 when the position of the liquid surface 81 is the highest. The state in which the position of the liquid surface 81 is highest is, for example, the state in which the liquid 80 is stored up to the full tank position of the container 70. Further, the length L2 and the length L3 are lengths determined by specifications such as the depth of the container 70, for example.

As shown in FIG. 4, if the length L1 is shorter than the length L2, it can be considered that the reflected internal propagation wave W1 and the surface wave W2 do not interfere with each other. However, the reflected internal propagating wave W1 and surface wave W2 are further reflected by the end portion 25 (and the piezoelectric element 31) of the propagating body 20 on the side closer to the piezoelectric element 31. Therefore, depending on the length L1, for example, when the reflected surface wave W2 first enters the piezoelectric element 31, a situation occurs in which the reflected surface wave W2 interferes with the internal propagating wave W1 reflected multiple times and enters the piezoelectric element 31. You can Even in this situation, it becomes difficult for the position determining unit 40 to determine which of the internal propagating wave W1 and the surface wave W2 reflected is input to the piezoelectric element 31.

Hereinafter, with reference to FIG. 5 and FIG. 6, the conditions for providing the internal propagating wave reflecting portion 22 at an appropriate position on the propagating body 20 will be described in consideration of this situation. The condition for providing the internal propagating wave reflection portion 22 at an appropriate position on the propagating body 20 is when the surface wave propagation velocity vr in the gas is faster and slower than the surface wave propagating velocity vlr in the liquid. different. First, with reference to FIG. 5, the condition when the propagating body 20 is made of a material whose surface wave propagation velocity vr in gas is faster than surface wave propagating velocity vlr in liquid will be described.

Of the reference numerals shown in FIGS. 5 and 6, the same reference numerals as those shown in FIG. 2 indicate the same terms as those described above with reference to FIG. Therefore, of the reference numerals shown in FIGS. 5 and 6, the same reference numerals as those shown in FIG. 2 will be omitted.

On the upper side of FIG. 5, the internal propagating wave W1 and the surface wave W2-E propagated by the propagating body 20 due to the vibration being generated in the state where the position of the liquid surface 81 is the lowest are reflected and input to the piezoelectric element 31. Is shown. The state where the position of the liquid surface 81 is the lowest is, for example, the state where the liquid 80 is below the position of the lowest line of the container 70. That is, in the situation shown on the upper side of FIG. 5, the propagating body 20 is not submerged in the liquid 80. Further, in the lower part of FIG. 5, the internal propagating wave W1 and the surface wave W2-F propagating by the propagating body 20 are reflected by the generation of vibration in the situation where the position of the liquid surface 81 is the highest, and the piezoelectric element is reflected. Inputting to 31 is shown. That is, in the situation shown on the lower side of FIG. 5, the propagation body 20 is immersed in the liquid 80 on the lower side of L3 shown in FIG.

NW1 shown in FIG. 5 is a reflected internal propagating wave input to the piezoelectric element 31 at a time point nt1 when a period nT1 obtained by multiplying the internal propagating wave propagation period T1 by n (n is an integer of 1 or more) has elapsed from t0. is there. That is, nW1 is an internal propagating wave that is reflected n times by the internal propagating wave reflector 22 and is input to the piezoelectric element 31.

A time point t2-E shown in FIG. 5 is a time point when the surface wave W2-E is reflected by the surface wave reflecting portion 24 and is input to the piezoelectric element 31. A time point t2-F shown in FIG. 5 is a time point when the surface wave W2-F is reflected by the surface wave reflecting portion 24 and is input to the piezoelectric element 31. The time points t2-E and t2-F are the time points at which the surface wave W2-E and the surface wave W2-F are reflected once by the surface wave reflecting portion 24 and input to the piezoelectric element 31. Further, the internal propagating wave nW1 and n at the time point nt1 are the number of times the internal propagating wave input to the piezoelectric element 31 is reflected by the internal propagating wave reflecting portion 22 immediately before the time point t2-E.

In the example shown in FIG. 5, the surface wave propagation velocity vr in the gas is faster than the surface wave propagation velocity vlr in the liquid, so that the time point t2-E is earlier than the time point t2-F. As a result, the surface wave propagation period T2-E in which the position of the liquid surface 81 is the lowest, which is the period from the time t0 to the time t2-E, is the surface wave propagation period T2 in which the position of the liquid surface 81 is the highest. Longer than -F.

(N+1)W1 shown in FIG. 5 is an internal propagating wave that is reflected by the internal propagating wave reflecting portion 22 once more than the internal propagating wave nW1 and is input to the piezoelectric element 31. The time (n+1)t1 shown in FIG. 5 is the time when the internal propagating wave (n+1)W1 is input to the piezoelectric element 31, that is, the time (n+1)T1 obtained by multiplying the internal propagating wave propagation period T1 by n+1 from t0 has elapsed. Is.

In the example shown in FIG. 5, the internal propagating wave nW1 does not overlap the surface wave W2-E and the surface wave W2-F, or the surface wave W2 between the surface waves W2-E and W2-F. By forming the internal propagating wave reflection portion 22 at the position on the propagating body 20 so as to satisfy such a condition, it is possible to determine whether the reflected internal propagating wave W1 or the surface wave W2 is input to the piezoelectric element 31. The position determination unit 40 can make an accurate determination.

In the example shown in FIG. 5, the position of the liquid surface 81 is the lowest in both the period nT1 obtained by multiplying the internal propagating wave propagation period T1 by n and the period (n+1)T1 obtained by multiplying the internal propagating wave propagation period T1 by n+1. Is not included between the surface wave propagation period T2-E at this time and the surface wave propagation period T2-F at the time when the position of the liquid surface 81 is the highest. By forming the internal propagating wave reflection portion 22 at the position on the propagating body 20 so as to satisfy such a condition, the reflected internal propagating wave W1 and the surface wave W2 do not interfere with each other.

When the propagating body 20 is made of a material in which the surface wave propagation velocity vr in gas is faster than the surface wave propagation velocity vlr in liquid, the internal propagating wave nW1 is the surface wave W2-E and the surface wave W2. The condition that -F or the surface wave W2 between the surface waves W2-E and W2-F does not overlap is that the following expressions (5) and (6) are established.

Here, since the relationship of period=length/speed holds, the equation (5) becomes the following equation (7), and the equation (6) becomes the following equation (8). However, in the formula, vs is the propagation velocity of the internal propagating wave W1, vr is the propagating velocity of the surface wave W2 in the gas, and vrr is the propagating velocity of the surface wave W2 in the liquid 80.

Equation (9) is obtained by rearranging Equations (7) and (8) as inequalities regarding L1.

By forming the internal propagating wave reflection part 22 in the propagating body 20 within the range of L1 that satisfies the expression (9), the internal propagating wave nW1 becomes the surface wave W2-E and the surface wave W2-F, or the surface wave. It does not overlap with the surface wave W2 between W2-E and the surface wave W2-F. Further, both the period nT1 obtained by multiplying the internal propagation wave propagation period T1 by n and the period (n+1)T1 obtained by multiplying the internal propagation wave propagation period T1 by n+1 are the surface wave propagation period T2- when the position of the liquid surface 81 is the lowest. It is not included between E and the surface wave propagation period T2-F when the position of the liquid surface 81 is the highest.

Next, with reference to FIG. 6, a condition when the propagating body 20 is made of a material whose surface wave propagation velocity vr in gas is slower than surface wave propagating velocity vlr in liquid will be described. Hereinafter, the same content as the condition described when the propagating body 20 is made of a material whose surface wave propagation velocity vr in gas is faster than the surface wave propagating velocity vlr in liquid described with reference to FIG. The description is omitted.

On the upper side of FIG. 6, when the position of the liquid surface 81 is the highest, the internal propagating wave W1 and the surface wave W2-F propagated by the propagating body 20 due to the generation of vibration are reflected and input to the piezoelectric element 31. Is shown. Further, on the lower side of FIG. 6, the internal propagating wave W1 and the surface wave W2-E propagating by the propagating body 20 are reflected by generating vibration in the state where the position of the liquid surface 81 is the lowest, and the piezoelectric element is reflected. Inputting to 31 is shown.

In the example shown in FIG. 6, since the surface wave propagation velocity vr in the gas is slower than the surface wave propagation velocity vlr in the liquid, the time point t2-E is later than the time point t2-F. .. As a result, the surface wave propagation period T2-E in which the position of the liquid surface 81 is the lowest, which is the period from the time t0 to the time t2-E, is the surface wave propagation period T2 in which the position of the liquid surface 81 is the highest. It is shorter than -F.

In the example shown in FIG. 6, as in the example shown in FIG. 5, the internal propagating wave nW1 is the surface wave W2-E and the surface wave W2-F, or between the surface wave W2-E and the surface wave W2-F. Surface wave W2 does not overlap. By forming the internal propagating wave reflection portion 22 at the position on the propagating body 20 so as to satisfy such a condition, it is possible to determine whether the reflected internal propagating wave W1 or the surface wave W2 is input to the piezoelectric element 31. The position determination unit 40 can make an accurate determination.

Also in the example shown in FIG. 6, both the period nT1 obtained by multiplying the internal propagation wave propagation period T1 by n and the period (n+1)T1 obtained by multiplying the internal propagation wave propagation period T1 by n+1, as in the example shown in FIG. Is not included between the surface wave propagation period T2-E when the position of the liquid surface 81 is the lowest and the surface wave propagation period T2-F when the position of the liquid surface 81 is the highest. By forming the internal propagating wave reflection portion 22 at the position on the propagating body 20 so as to satisfy such a condition, the reflected internal propagating wave W1 and the surface wave W2 do not interfere with each other.

When the propagating body 20 is made of a material in which the surface wave propagation velocity vr in gas is slower than the surface wave propagation velocity vlr in liquid, the internal propagating wave nW1 is the surface wave W2-E and the surface wave W2. The condition that -F or the surface wave W2 between the surface waves W2-E and W2-F does not overlap is that the following expressions (10) and (11) are satisfied.

Equation (12) is obtained by modifying Equations (10) and (11) in the same manner as Equations (5) and (6) described above, and then rearranging them as inequalities regarding L1.

By forming the internal propagating wave reflection part 22 in the propagating body 20 within the range of L1 that satisfies the expression (12), the internal propagating wave nW1 is the surface wave W2-E and the surface wave W2-F, or the surface wave. It does not overlap with the surface wave W2 between W2-E and the surface wave W2-F. Further, both the period nT1 obtained by multiplying the internal propagation wave propagation period T1 by n and the period (n+1)T1 obtained by multiplying the internal propagation wave propagation period T1 by n+1 are the surface wave propagation period T2- when the position of the liquid surface 81 is the lowest. It is not included between E and the surface wave propagation period T2-F when the position of the liquid surface 81 is the highest.

In the example shown in FIGS. 5 and 6, when the amplitude of the internal propagating wave (n+1)W1 is smaller than the predetermined amplitude, the internal propagating wave reflection unit 22 uses the following Expression (13) instead of Expression (9). Alternatively, instead of Expression (12), L1 may be provided within the range so as to satisfy the following Expression (14). When the amplitude of the internal propagating wave (n+1)W1 is smaller than the predetermined amplitude, for example, the vibration detection unit 33 inputs the voltage output from the piezoelectric element 31 to the piezoelectric element 31 to the extent that the voltage cannot be accurately detected. This is when the amplitude of the internally propagating wave becomes smaller.

When the amplitude of the internal propagating wave (n+1)W1 is smaller than the predetermined amplitude, the internal propagating wave reflector 22 is formed in the propagating body 20 within the range of L1 that satisfies the expression (13) or the expression (14). As a result, the internal propagating wave nW1 does not overlap the surface wave W2-E and the surface wave W2-F, or the surface wave W2 between the surface waves W2-E and W2-F. Further, both the period nT1 obtained by multiplying the internal propagation wave propagation period T1 by n and the period (n+1)T1 obtained by multiplying the internal propagation wave propagation period T1 by n+1 are the surface wave propagation period T2- when the position of the liquid surface 81 is the lowest. It is not included between E and the surface wave propagation period T2-F when the position of the liquid surface 81 is the highest.

Further, in the example shown in FIGS. 5 and 6, n is 1 when the length of L1 is longer than half the length of L2. The amplitude of the internal propagating wave W1 becomes smaller as the number of times of reflection by the internal propagating wave reflecting portion 22 increases. That is, when n, which is the number of times the internal propagating wave W1 is reflected by the internal propagating wave reflector 22, is 1, the amplitude of the internal propagating wave W1 input to the piezoelectric element 31 is the largest, and the position determiner 40 detects the amplitude. Is easy.

Further, as the number of times reflected by the internal propagating wave reflecting section 22 increases, the amplitude of the internal propagating wave W1 decreases, so that the number of times the internal propagating wave reflecting section 22 reflects, that is, n is preferably 5 or less.

In the present embodiment, the internal propagating wave reflection portion 22 is formed by the notched groove 21, but the present invention is not limited to this embodiment, and any configuration that reflects the internal propagating wave W1 may be used. The configuration in which the internal propagating wave W1 is reflected may be, for example, a through hole, a part of the propagating body 20 cut out to the bottom surface in a key shape, a screw stopper, or a member in which the groove 21 is fitted. Good. Further, another member fitted into the groove 21 may be resin or metal.

The present invention is not limited to the above-described exemplary embodiments, and those skilled in the art can easily modify the above-described exemplary embodiments to the scope included in the claims. ..

DESCRIPTION OF SYMBOLS 10... Liquid surface position detection device, 20... Propagator, 21... Groove, 22... Internal propagation wave reflection part, 24... Surface wave reflection part, 31... Piezoelectric element, 32 ...Vibration generator, 33...Vibration detector, 40...Position determining unit, 50...Case, 70...Container, 80...Liquid, 81...Liquid level, W1. ..Internally propagating waves, W2... surface waves.

Claims (4)

A vibration generating section that vibrates the piezoelectric element by applying a voltage to the piezoelectric element;
A propagating body that propagates the vibration of the piezoelectric element,
A vibration detector that detects that the vibration is reflected by the reflector of the propagator and is input to the piezoelectric element,
A position determining unit that determines the position of the liquid surface of the liquid in which the propagating body is immersed;
A liquid surface position detecting device comprising:
The propagating body propagates a surface wave in which the vibration propagates on the surface of the propagating body, and an internal propagating wave in which the vibration propagates inside the propagating body,
The reflecting portion includes a surface wave reflecting portion and an internal propagating wave reflecting portion,
The position determining unit is immersed in the propagating body based on a surface wave propagation period, which is a period from when the vibration is generated to when the surface wave is reflected by the surface wave reflecting unit and is input to the piezoelectric element. Determining the position of the liquid surface of the liquid,
The position determining unit propagates the surface wave by an internal propagating wave propagation period which is a period from when the vibration is generated to when the internal propagating wave is reflected by the internal propagating wave reflecting unit and is input to the piezoelectric element. Correct the period,
The surface acoustic wave reflection portion is one of two end portions in the longitudinal direction of the propagating body, which is farther from the piezoelectric element.
The internal propagating wave reflector is formed at a position on the propagating body such that a period obtained by multiplying the internal propagating wave propagation period by n (n is an integer of 1 or more) does not overlap with the surface wave propagating period , The surface when the position of the liquid surface of the liquid in which the propagating body is immersed is highest in both the period in which the internal propagating wave propagation period is multiplied by n and the period in which the internal propagating wave propagation period is multiplied by n+1 as it not included between said surface wave propagation period when the position of the liquid surface of the liquid in which the propagating body and the wave propagation time is immersed lowest, Ru is formed at a position on the propagation member A liquid surface position detection device characterized by the above. The internal propagating wave reflector is positioned on the propagating body so as to satisfy the following equation (1) when the propagation velocity of the surface wave in the gas is higher than the propagating velocity of the surface wave in the liquid. On the other hand, when the propagation velocity of the surface wave in the gas is slower than the propagation velocity of the surface wave in the liquid, the position on the propagating body is set so as to satisfy the following equation (2). is formed, claim 1 Symbol placement ink surface position detecting apparatus.

here,
vs is the propagation velocity of the internal propagating wave,
vr is the propagation velocity of the surface wave in the gas,
vlr is the propagation velocity of the surface wave in the liquid,
L1 is the length from the end of the propagating body closer to the piezoelectric element to the internal propagating wave reflection portion,
L2 is the total length of the propagator,
L3 is the length from the end of the propagating body on the side closer to the piezoelectric element to the position of the liquid surface when the position of the liquid surface is the highest. When the amplitude of the internal propagating wave that is reflected by the internal propagating wave reflector and is input to the piezoelectric element at the time point when the internal propagating wave propagation period is multiplied by n+1 is smaller than a predetermined amplitude,
The internal propagating wave reflection unit is configured to satisfy the following formula (3) instead of the formula (1) or the following formula (4) instead of the formula (2). The liquid level position detecting device according to claim 2 , which is formed at an upper position.

The n is 1 when the length from the end of the propagating body closer to the piezoelectric element to the internal propagating wave reflection portion is longer than half the total length of the propagating body. 3. The liquid surface position detection device according to any one of 3 above.

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