WO2016104415A1

WO2016104415A1 - Ultrasonic sensor

Info

Publication number: WO2016104415A1
Application number: PCT/JP2015/085653
Authority: WO
Inventors: 浩司南部
Original assignee: 株式会社村田製作所
Priority date: 2014-12-26
Filing date: 2015-12-21
Publication date: 2016-06-30
Also published as: CN107113511A; KR20170085104A; JP6493415B2; CN107113511B; JPWO2016104415A1; KR101935784B1

Abstract

An ultrasonic sensor (101) is provided with the following: a bottomed cylindrical case (2) having a bottom plate (2a) and side walls (2b); a piezoelectric element (3) disposed above the bottom plate (2a) inside the case (2); and a filling resin (8) filled into at least a portion of the inside of the case (2), so as to cover the piezoelectric element (3) inside the case (2). Among the inner surfaces of the case (2), at least a surface with which the filling resin (8) makes contact is a rough surface.

Description

Ultrasonic sensor

The present invention relates to an ultrasonic sensor.

An ultrasonic sensor may be used to measure the presence or absence of an object and the distance to the object. An example of an ultrasonic sensor based on the prior art is described in International Publication WO2013 / 051525A1 (Patent Document 1). In this ultrasonic sensor, a piezoelectric element is arranged inside a bottomed cylindrical case. The piezoelectric element has a flat plate shape and is disposed on the bottom surface of the case. Wiring is provided so that a voltage can be applied to both surfaces of the piezoelectric element. This type of ultrasonic sensor can transmit and receive ultrasonic waves. When transmitting ultrasonic waves, a voltage is applied to the plate-like piezoelectric element, so that the piezoelectric element vibrates in the plane direction, and this vibration is transmitted to vibrate the bottom plate of the case in a direction perpendicular to the plane. Ultrasonic waves are emitted to the outside by the vibration of the bottom plate of the case. When receiving the ultrasonic wave, the bottom plate of the case is vibrated by the ultrasonic wave reaching from the outside, and this vibration is transmitted to the piezoelectric element as a vibration in the surface direction of the piezoelectric element. As a result, a potential change occurs and is detected electrically.

International Publication WO2013 / 051525A1

Generally, when this type of ultrasonic sensor is used, a pause time is provided after a certain transmission time, and reception is performed during this time. That is, after the piezoelectric element is continuously vibrated by applying a potential change to the piezoelectric element for a certain time, the potential change is stopped, and thereafter, the vibration generated in the piezoelectric element by reception is electrically detected. However, the vibration generated from the piezoelectric element during transmission not only vibrates the bottom plate of the case, but also vibrates the side wall of the case at the same time. Even after the supply of the potential change to the piezoelectric element is stopped, the side wall of the case may continue to vibrate. Such vibration remaining in the case is also referred to as “reverberation vibration”. The time that the reverberation continues continues is also called “reverberation time”. When measuring with an ultrasonic sensor in a state where the distance to the object is short, since the ultrasonic wave emitted from the ultrasonic sensor and reflected by the object returns to the ultrasonic sensor at an early stage, reverberation Reception may occur before the time expires. During reception, what should be detected is vibration generated in the bottom plate due to the ultrasonic wave reflected by the object (hereinafter referred to as “reflected wave”). When reaching the bottom plate, the vibration caused by the reflected wave is buried in the reverberation vibration that was originally there. In this case, the detection characteristics of the ultrasonic sensor deteriorate, and in the worst case, the reflected wave cannot be detected.

In order to obtain good detection characteristics with an ultrasonic sensor even when the distance to the object is short, it is required to shorten the reverberation time as much as possible.

Therefore, an object of the present invention is to provide an ultrasonic sensor in which reverberation time is shortened while maintaining sensitivity.

To achieve the above object, an ultrasonic sensor according to the present invention includes a bottomed cylindrical case having a bottom plate and a side wall, a piezoelectric element disposed on the bottom plate in the case, and the above-described case in the case. A filling resin filled in at least a part of the case so as to cover the piezoelectric element, and at least a surface of the case in contact with the filling resin is a rough surface. Thereby, it is possible to realize an ultrasonic sensor with a reverberation time shortened while maintaining the sensitivity of the ultrasonic sensor.

In the above invention, the inner surface of the side wall is preferably a rough surface. Thereby, the vibration damping property of the side wall of the case is improved, and an ultrasonic sensor with a short reverberation time can be realized.

Preferably, in the above invention, the entire surface of the inner surface of the bottom plate and the inner surface of the side wall is a rough surface. Thereby, an ultrasonic sensor with a shorter reverberation time can be realized.

In the above invention, the surface roughness Ra of the rough surface is preferably 1.3 μm or more and 2.2 μm or less. Thereby, the reverberation characteristic can be improved without reducing the sensitivity of the ultrasonic sensor.

In the above invention, the rough surface is preferably formed by sandblasting. Thereby, a desired rough surface can be easily formed in a case.

In the above invention, preferably, the case is made of an aluminum alloy. Thereby, a case becomes easy to process and a desired rough surface can be formed easily. Further, by forming the case with such a material, the weight of the ultrasonic sensor as a whole can be reduced.

According to the present invention, it is possible to realize an ultrasonic sensor in which reverberation time is shortened while maintaining sensitivity.

It is sectional drawing of the ultrasonic sensor in Embodiment 1 based on this invention. It is a graph which shows the profile of a case bottom face when not performing sandblasting to a case inner surface. It is a graph which shows the profile of a case bottom surface when sandblasting is performed to the case inner surface and surface roughness Ra is 2.02 micrometers. It is a graph which shows the relationship between surface roughness and reverberation time. It is sectional drawing of the ultrasonic sensor in Embodiment 2 based on this invention. It is a graph which shows the relationship between the surface roughness and the fluctuation value from the reference | standard of resonance frequency.

(Embodiment 1)
With reference to FIG. 1, the ultrasonic sensor in Embodiment 1 based on this invention is demonstrated. In the following description, the vertical relationship in FIG. 1 will be described as a reference, but the term “upper and lower” here does not mean absolute upper and lower, but is merely for convenience of explanation, and in the posture shown in FIG. It is up and down.

The ultrasonic sensor 101 in the present embodiment includes a case 2, a piezoelectric element 3, a sound absorbing material 4, a reinforcing material 5, a damper 7, a filling resin 8, a flexible substrate 9, a terminal holding member 10,

Pin terminals

11 and 11 and

lead wires

12 and 12 are provided.

Case 2 is made of, for example, lightweight aluminum with a high elastic modulus. Case 2 is formed by forging, for example. The case 2 has a bottomed cylindrical shape in which one end face is closed and the other end face is opened. The outer shape of the case 2 has a bottom surface with a diameter of 15.5 mm and a height of 9.0 mm. The case 2 has, for example, a disk-shaped bottom plate 2a and a cylindrical side wall 2b. The opening of the case 2 is circular when viewed in plan, for example. Side wall 2b includes a thin portion and a thick portion. The portion on the opening side of the side wall 2b is thin, and the portion on the bottom plate 2a side is thick. Accordingly, the inner diameter (diameter 12.0 mm) of the portion of the side wall 2b on the bottom plate 2a side is smaller than the inner diameter (diameter 14.5 mm) of the portion on the opening side of the side wall 2b. The bottom plate 2a has a recess in the vicinity of the center. The depth of the recess is, for example, 0.49 mm. The material of the case 2 is not limited to a conductive material such as aluminum, and may be an insulating material. Fine irregularities are formed on the inner surface of the bottom plate 2a of the case 2 and the inner surface of the side wall 2b of the case so as to be a rough surface having a larger surface roughness than the outer surface of the side wall of the case. Of the inner surface of the case, at least the surface in contact with the filling resin is a rough surface.

The piezoelectric element 3 is made of, for example, lead zirconate titanate ceramic. The piezoelectric element 3 has a disk-shaped piezoelectric body and a pair of electrodes provided on the principal surfaces of the piezoelectric body facing away from each other. The piezoelectric element 3 has a flat plate shape, and “spreads and vibrates” in the in-plane direction when a driving voltage is applied to a pair of electrodes. The piezoelectric element 3 is disposed in the recess of the case 2 and joined to the bottom plate 2a. Specifically, the piezoelectric element 3 is joined to the case 2 so that one of the pair of electrodes is in contact with the bottom surface of the recess.

The piezoelectric element 3 and the bottom plate 2a are joined together to form a bimorph vibrator. This bimorph vibrator is bent and vibrated by the spreading vibration of the piezoelectric element 3. Therefore, the bottom plate 2 a becomes the main vibration region of the case 2.

The sound absorbing material 4 is made of, for example, polyester felt. The sound absorbing material 4 has a flat plate shape, for example. The sound absorbing material 4 is provided so as to cover the piezoelectric element 3. The sound absorbing material 4 is provided to absorb unnecessary sound waves emitted from the piezoelectric element 3 to the opening side of the case 2.

The reinforcing material 5 is a ring-shaped member having an opening at the center, and has high acoustic impedance. The reinforcing material 5 is made of a material having a higher density and higher rigidity than the material constituting the case 2 and functions as a weight. The material of the reinforcing material 5 may be stainless steel or zinc, for example. The reinforcing material 5 may be made of the same material (aluminum) as the case 2 by adjusting the size such as thickness. The reinforcing material 5 is provided above the sound absorbing material 4 so as to be separated from the sound absorbing material 4. The reinforcing material 5 is held by a step provided on the inner surface of the case 2. Specifically, the reinforcing material 5 is disposed in contact with the inner surface of the thick portion of the side wall 2b. By providing the reinforcing material 5 in this way, the rigidity of the case 2 is increased, and the vibration in the bottom plate 2a of the case 2 can be prevented from being transmitted to the side wall 2b of the case 2. Since the internal space of the case 2 is partitioned by the reinforcing material 5, the sound absorbing material 4 is surrounded by a cavity 13.

The damper 7 is a cup-shaped member made of an elastic body such as silicone rubber or urethane resin. The damper 7 has a convex portion that engages with the opening of the reinforcing member 5 and an opening that extends upward from the convex portion and engages with the terminal holding member 10.

One end of each of the

lead wires

12 and 12 is connected to a flexible substrate 9 to be described later, and is inserted into the damper 7 and disposed in the opening of the case 2. The other ends of the

lead wires

12 and 12 are arranged outside the case 2 and connected to the terminal holding member 10.

The terminal holding member 10 is an L-shaped member made of a resin such as polybutylene terephthalate (PBT). Two through holes into which the

pin terminals

11 and 11 are inserted are provided in the center portion of the terminal holding member 10.

The

pin terminals

11 and 11 are metal linear pins to which the driving voltage of the piezoelectric element 3 is applied, and are held by the terminal holding member 10. Specifically, the

pin terminals

11 and 11 are inserted into the through holes of the terminal holding member 10 and connected to the

lead wires

12 and 12, respectively.

The flexible substrate 9 has a wide band shape, and electrically connects the

lead wires

12 and 12 and the piezoelectric element 3. The flexible substrate 9 has a first end and a second end. The first end is connected to the

lead wires

12 and 12. The second end is connected to the electrode of the piezoelectric element 3 by a conductive adhesive. The flexible substrate 9 is bent and disposed in the opening of the case 2.

The filling resin 8 is made of an elastic body such as silicone resin or urethane resin. The filling resin 8 is filled in at least a part of the case 2 so as to cover the piezoelectric element 3 inside the case 2. Specifically, the filling resin 8 is filled in the entire space above the reinforcing material 5 in the internal space of the case 2. The filling resin 8 seals the reinforcing material 5, the damper 7, one end of the

lead wires

12, 12 and the flexible substrate 9 disposed in the opening of the case 2.

The filling resin 8 has a function of suppressing vibration of the side wall 2b of the case 2 and also has a function of preventing the

lead wires

12, 12 and the damper 7 from being detached from the case 2.

The damper 7 is more suitable if it is difficult to propagate vibration. The filling resin 8 is more preferable as long as it suppresses (vibrates) the vibration of the side wall 2a of the case 2. The damper 7 preferably has a lower elastic modulus than the filled resin 8. More specifically, the elastic modulus includes a storage elastic modulus and a loss elastic modulus. It is preferable that the damper 7 has a small storage elastic modulus and the filling resin 8 has a large loss elastic modulus. For example, the damper 7 is preferably made of a silicone resin (silicone rubber). The filling resin 8 is preferably made of a urethane resin.

According to the present embodiment, since at least the surface of the inner surface of the case that is in contact with the filling resin is a rough surface, the ultrasonic sensor with the reverberation time shortened while maintaining the sensitivity of the ultrasonic sensor. Can be realized. In order to verify this effect, the following experiment was conducted as Experiment 1.

(Experiment 1)
In Experiment 1, the effect of the presence and degree of rough surface formation is confirmed. The ultrasonic sensors with condition numbers 1 to 6 that are samples used in this experiment will be described in detail below.

First, a plurality of cases manufactured under the same conditions were prepared. Of these, no additional work was performed on the case of condition number 1. A rough surface was formed by sandblasting under different conditions on the inner surface of the bottom plate of the case of condition numbers 2 to 6 and the inner surface of the side wall of the case (hereinafter simply referred to as “inner surface of the case”). Table 1 shows the sandblast conditions for the case and the surface roughness Ra for each condition number. The surface roughness referred to here is the roughness of the inner surface of the case. The surface roughness Ra of Condition No. 1 was 1.0 μm. The surface roughness Ra under condition numbers 2 to 6 were 1.3 μm, 1.6 μm, 2.0 μm, 2.2 μm, and 2.5 μm, respectively.

FIG. 2 shows a surface roughness profile with respect to the position of the inner surface of the bottom plate of the case of condition number 1. FIG. 3 shows a surface roughness profile with respect to the position of the inner surface of the bottom plate of the case of condition number 5. In FIG. 1, the horizontal axis represents the distance T1 of the inner surface of the bottom plate of the case. The left end of T1 in FIG. 1 corresponds to the position 0 μm, and the right end of T1 in FIG. 1 corresponds to the position 1200 μm. Comparing FIG. 2 and FIG. 3, it can be seen that condition number 5 subjected to sandblasting has a narrower width of unevenness on the inner surface of the bottom plate of the case and larger variation in unevenness depth than condition number 1. . Next, an ultrasonic sensor (condition numbers 1 to 6) having the same configuration as the ultrasonic sensor of the first embodiment was assembled using the above-described case. These ultrasonic sensors were driven at a frequency of 40.0 kHz, for example, and the reverberation time was measured with an oscilloscope. The ultrasonic sensors of condition numbers 1 to 6 are the same for members other than the case. The measurement conditions are all the same.

For each condition, five experiments were performed with the prepared sample, and the average value of the obtained reverberation time was defined as the length of the reverberation time corresponding to the condition. The results are summarized as shown in FIG. The reverberation times for condition numbers 1 to 6 were 1.77 msec, 1.71 msec, 1.63 msec, 1.60 msec, 1.57 msec, and 1.52 msec, respectively. Therefore, it has been found that the reverberation time becomes shorter as the surface roughness Ra of the inner surface of the case increases.

From this, it can be said that the reverberation time is shortened in the ultrasonic sensor in which the inner surface of the case 2 is roughened compared to the case in which the inner surface of the case 2 is not roughened. It is considered that the vibration contact property in the case 2 is improved and the reverberation can be suppressed at an early stage because the surface of the inner surface of the case 2 that is in contact with the filling resin 8 is a rough surface. Therefore, the ultrasonic sensor in the present embodiment is an ultrasonic sensor with a reverberation time shortened.

(Experiment 2)
The inventor examined the resonance frequency at each surface roughness as Experiment 2 using the sample of Experiment 1. The reference resonance frequency is the resonance frequency of condition number 1. As a result, the relationship between the surface roughness of the rough surface provided on the inner surface of the case 2 and the resonance frequency is as shown in FIG. The fluctuation values from the reference of the resonance frequency of condition numbers 2 to 6 were −0.10 kHz, −0.28 kHz, −0.36 kHz, −0.50 kHz, and −1.03 kHz, respectively. The inventor has found that the resonance frequency fluctuates outside the original value of 40.0 kHz in the sample with the increased surface roughness Ra. As shown in FIG. 6, it was found that the resonance frequency decreases as the surface roughness Ra increases. Further, when the surface roughness Ra is increased in order, the sample having a surface roughness Ra larger than 2.2 μm, for example, the surface roughness Ra, compared to a sample having a surface roughness Ra of 2.2 μm or less. In the sample of 2.5 μm, it was found that the resonance frequency was particularly greatly varied and decreased. When the resonance frequency is reduced, the sensitivity is lowered, so that even if the reverberation characteristics are improved, the characteristics of the ultrasonic sensor as a whole are deteriorated.

According to FIG. 4, it is known that the surface roughness Ra of the inner surface of the case 2 may be increased in order to shorten the reverberation time. However, from the tendency shown in FIG. 6, the surface roughness Ra is increased. If too much, it can be seen that the adverse effect of increasing the fluctuation range of the resonance frequency is brought about. Therefore, in order to realize an ultrasonic sensor with a reverberation time shortened while maintaining the sensitivity of the ultrasonic sensor, the surface roughness Ra of the rough surface is preferably 1.3 μm or more and 2.2 μm or less.

(Embodiment 2)
With reference to FIG. 5, the ultrasonic sensor in Embodiment 2 based on this invention is demonstrated. The configuration of the ultrasonic sensor 102 in the present embodiment is basically the same as the configuration of the ultrasonic sensor 101 described in the first embodiment, but differs in the following points.

In the ultrasonic sensor 102, the sound absorbing material 4, the reinforcing material 5, and the damper 7 are not arranged inside the case 2. Further, the cavity 13 is not provided inside the case 2. Filling resin 8 is filled so as to cover the piezoelectric element 3 disposed so as to be in contact with the bottom plate 2 a inside the case 2. Of the inner surface of the case 2, at least the surface in contact with the filling resin 8 is a rough surface. Therefore, in the present embodiment, at least almost all of the inner surface of the case 2 is a rough surface.

For example, it is preferable that the inner surface of the bottom plate 2a and the inner surface of the side wall 2b are rough.

In the present embodiment, an ultrasonic sensor having a reverberation time shorter than that in the first embodiment can be realized.

The rough surface is preferably formed by sandblasting. This is because, as already shown in the experiment of the first embodiment, when sandblasting is employed, a rough surface can be easily formed on the inner surface of the case 2.

Case 2 is preferably formed of an aluminum alloy. By adopting this configuration, the case 2 is easy to process, and a desired rough surface is easily formed. Further, by forming the case 2 with such a material, the weight of the ultrasonic sensor as a whole can be reduced.

In each of the above-described embodiments, the example in which the electrical lead-out from the case 2 is performed by the lead wire 12, the pin terminal 11, and the like has been described. However, the electrical lead-out may be realized by other configurations. .

In addition, you may employ | adopt combining suitably two or more among the said embodiment.
In addition, the said embodiment disclosed this time is an illustration in all the points, Comprising: It is not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

2 case, 2a bottom plate, 2b side wall, 3 piezoelectric element, 4 sound absorbing material, 5 reinforcing material, 7 damper, 8 filling resin, 9 flexible substrate, 10 terminal holding member, 11 pin terminal, 12 lead wire, 13 cavity, 101, 102 Ultrasonic sensor.

Claims

A bottomed cylindrical case having a bottom plate and side walls;
A piezoelectric element disposed on the bottom plate in the case;
A filling resin filled in at least a part of the case so as to cover the piezoelectric element in the case;
An ultrasonic sensor in which at least a surface of the inner surface of the case that is in contact with the filling resin is a rough surface.
The ultrasonic sensor according to claim 1, wherein an inner surface of the side wall is a rough surface.
The ultrasonic sensor according to claim 2, wherein an inner surface of the bottom plate is a rough surface.
The ultrasonic sensor according to any one of claims 1 to 3, wherein a surface roughness Ra of the rough surface is 1.3 µm or more and 2.2 µm or less.
The ultrasonic sensor according to any one of claims 1 to 4, wherein the rough surface is formed by sandblasting.
The ultrasonic sensor according to any one of claims 1 to 5, wherein the case is formed of an aluminum alloy.