JP2002228742A - Ultrasonic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic sensor easily usable even if a fitting space in rear of the sensor in the axial direction thereof is relatively narrow. SOLUTION: A bottomed case is formed of a plastic case part provided with an adjustable layer and a metal case part to be bonded to the bottomed case part for sealing and forming a piezoelectric element housing space together with the bottomed case part. The piezoelectric element provided with electrodes in an upper and a lower surfaces thereof is fitted to the inner bottom surface of the bottomed case part and external shield wires to be electrically connected to both electrodes of the piezoelectric element are taken out of a side surface of the metal case part. An open end of the metal case part is filled with a sealing material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor using a piezoelectric element which can be used, for example, as a gas sensor.

[0002]

2. Description of the Related Art As this type of ultrasonic sensor, a metal case type and a resin case type are known. Generally, the former is excellent in weather resistance and moisture resistance, and the latter is an electric sensor. Excellent sound conversion efficiency, high sensitivity and excellent responsiveness.

As an example of a metal case type ultrasonic sensor,
Japanese Patent Application Laid-Open No. 61-191198 has a case in which a piezoelectric element is joined to the inner bottom surface of a metal case, and a base in which input / output terminals are planted. An electrode in which the electrode is electrically connected to an input / output terminal of a base portion is disclosed.

[0004] As an example of a resin case type ultrasonic sensor, Japanese Utility Model Registration No. 1778125 discloses that a piezoelectric element is attached to the center of the inner bottom surface of a case made of a foamable plastic material, A type in which the provided electrode is connected to a connection element that leads to the outside and the opening of the case is closed with a lid member is disclosed. High acoustic attenuation is achieved by using a foamable plastic material having a low Q value for the case. As a result, the reverberation time can be significantly reduced, and a highly sensitive sensor can be provided.

[0005] In either of these types, generally,
An input / output terminal and an input / output cable that are electrically connected to the electrodes of the piezoelectric element are provided so as to extend along the sensor axial direction through a cover member or a base portion of the sensor.
Therefore, there is a need for a sufficient space behind the base of the sensor to route the input / output terminals and input / output cables.

[0006]

By the way, such an ultrasonic sensor is usually limited in a mounting base depending on a mounting portion in a used mechanical device such as an automobile, a measuring instrument and an industrial robot. Therefore, there may be a case where a sufficient space for the input / output terminal and the input / output cable cannot be secured.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ultrasonic sensor which can solve the above-mentioned problems of the conventional structure and can be easily used even when the space behind the sensor in the axial direction is relatively narrow. And

[0008]

In order to achieve the above-mentioned object, an ultrasonic sensor according to the present invention comprises a bottomed case portion made of a plastic material forming a part of a case and forming a matching layer; It has a metal case part that is hermetically bonded to the case part and defines a space for accommodating the piezoelectric element together with the bottomed case part, and a piezoelectric element with electrodes on both the upper and lower surfaces is attached to the inner bottom surface of the bottomed case part The outer shield is electrically connected to both electrodes of the piezoelectric element, and is taken out from the side of the outer shield. The open end of the metal case is filled with a sealing material.

In a preferred embodiment, a shield member is arranged around the piezoelectric element, a relay substrate is provided at a free end of the shield member, and both electrodes of the piezoelectric element and an external shield wire are connected to a relay terminal formed on the relay substrate. Respectively.

[0010] The side length of the bottomed case portion and the side length of the metal case portion can be set so that the total length of the side lengths is an integral multiple of λ / 4.

In a further preferred embodiment, the encapsulant may be filled over a sponge member layer provided over the open end of the metal case part.

Further, in the ultrasonic sensor according to the present invention, the gap between the jacket at the outer end of the outer shield wire and each conductor exposed therefrom can be sealed by a sealing member.

In the ultrasonic sensor according to the present invention having the above-described configuration, the external shield wire is drawn out to the side of the metal case portion, so that the external shield wire can be routed rearward in the axial direction of the sensor. This space is not required, and the flexibility and adaptability of the sensor mounting can be greatly improved.

A shield member is provided in the case so as to surround the periphery of the piezoelectric element. On a relay board provided at a free end of the shield member, a conductive wire from both electrodes of the piezoelectric element and an external shield wire are electrically connected. When the connection is configured, it is easy to assemble the wiring inside the case, and at the same time, even if external stress is applied to the external shield wire, it is received by the relay board, and force is applied to the conductive wires leading to both electrodes of the piezoelectric element. Without
The vibration of the piezoelectric element is not hindered.

Further, by setting the respective side lengths of the bottomed case portion and the metal case portion such that the total length of the side lengths is an integral multiple of λ / 4, from the bottom surface of the bottomed case portion to the side surface. The phase of the leaked vibration and the phase of the vibration reflected back to the opening of the main part of the metal case part are opposite to each other and are canceled out, suppressing the vibration on the entire side of the case and improving the sensitivity and output. it can.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an ultrasonic sensor according to an embodiment of the present invention.
The case is formed of a bottomed case part 1 having a cylindrical cross section made of a plastic material and a metal case part 2 having a cylindrical cross section sealed and joined to the bottomed case part 1, and has a piezoelectric element 3 inside. It defines the space to house. The bottomed case part 1 of the case forms a matching layer, and its outer end face is
A region corresponding to the piezoelectric element 3 protrudes. The metal case part 2 having a cylindrical cross section can be made of aluminum.

As shown in FIG.
Is usually set to the same thickness as the length of λ / 4 (indicated by the dashed line A). The side length of the case portion 1 and the side length of the metal case portion 2 are set to λ / 4 or an integral multiple thereof, respectively, and in this embodiment, the sound speed is 300 m / s.
The side length of the bottomed case part 1 made of plastic material is λ
/ 2 length, the side length of the metal case portion 2 made of metal having a sound velocity of 600 m / s was set to λ / 4 length, and the entire side length was set to 3λ / 4 length. With this configuration, the phase of vibration leaking from the bottom surface of the bottomed case to the side surface, as shown by the dashed lines b and b, and the vibration reflected from the upper opening surface of the metal case and returning. The phase b 'cancels each other, the vibration of the side surface of the entire case is absorbed, and the sensitivity and the output are increased.

As shown, the piezoelectric element 3 is fixed to the inner bottom of the bottomed case portion 1 with an adhesive, and conductive layers 3a and 3b for forming electrodes are formed on the upper and lower surfaces.
A shield member 4 including a side periphery of the piezoelectric element 3 is arranged along the inner peripheral wall of the bottomed case portion 1. One end of the shield member 4 is closed by an end wall 4a except for a central portion, and a relay board 5 is mounted inside the end wall 4a of the shield member 4. The relay board 5 has a central opening 5a as shown.

As shown in FIG. 2, a notch groove 2a having a predetermined depth is formed at the side end of the metal case portion 2 having a cylindrical cross section, and the other end of the outer shield wire 6 is formed from the notch groove 2a. It is derived outward. Each conductor 6a, 6b, 6c exposed from one end of the outer shield wire 6 is electrically connected to the corresponding terminal 5a, 5b, 5c formed on the relay board 5, and the terminals 5a, 5b of the relay board 5 are , Conducting wires 7a, 7
The electrodes on both the upper and lower surfaces of the piezoelectric element 3 are electrically connected via b. In this case, the terminal 5c of the relay board 5 is a ground terminal. The distance between the relay board 5 and the piezoelectric element 3 is
The conductors 6 a and 6 b and the conductors 7 a and 7 b of the shield wire 6 are determined so as to ensure that they do not contact the piezoelectric element 3.
The depth of the cutout groove 2a is set to be equal to or slightly larger than the outer dimension of the outer shield wire 6 so as not to protrude from the upper opening surface of the metal case portion 2.

In the sensor assembly thus mounted,
A sponge plate 8 such as paper phenol is provided on the relay board 5 in the case portion 2 with a gap between the sponge board 8 and the relay board 5, and a sealing material 9 is filled from above with a sealing wire 6 embedded therein. You. Therefore, the shield wire 6 is hermetically fixed and supported by the sealing material 9. In this case, as the sealing material 9, an epoxy resin or a urethane resin containing ceramic powder can be used.

FIG. 3 shows a shield wire, that is, a stripped portion 10 of an insulating jacket 6d at the outer end of the external cable 6, and a resin molding material 11 covering a part of the conductive wires 6a, 6b and 6c exposed thereby. Is applied and solidified by heat treatment to prevent moisture from entering through gaps between the insulating jacket 6d and the conductive wires 6a, 6b, 6c. It should be noted that the cut line of the stripped portion 10 of the external cable is not made into a uniform straight line, but is made into a rough (rough) line having irregularities (zigzag) as shown in the figure, so that the adhesion to the mold material 11 can be improved. (Anchor effect) is not always necessary.

Next, FIG. 4 shows another method of sealing the peeled portion 10 of the external cable 6, which is a heat-shrinkable tube having a hot-melt adhesive layer 12a made of a thermoplastic resin on the inner surface as a sealing member. 12 and the stripped portion 10 of the external cable 6 and the exposed conductors 8a and 8b.
Is wound so as to cover a part of the wire, the adhesive layer 12a is melted by heat treatment, and the gap between the conductive wires 6a, 6b, and 6c is filled and the heat-shrinkable tube 12 is shrunk and adhered. The sealing operation is simpler and more reliable than in the embodiment of FIG.

[0023]

As described above, in the ultrasonic sensor according to the present invention, the case is hermetically joined to the bottomed case portion made of a plastic material having a matching layer and the bottomed case portion. And a metal case part that defines a space for accommodating the piezoelectric element, and a piezoelectric element having electrodes on both the upper and lower surfaces is attached to the inner bottom surface of the bottomed case part and connected to both electrodes of the piezoelectric element. The outer shield wire is configured to be drawn out to the side of the metal case part, and the open end of the metal case part is filled with a sealing material. No space is required behind the sensor in the axial direction of the sensor for routing the external shield wire.This greatly improves the flexibility and adaptability of sensor mounting. So that it is. In addition, even when an external stress is applied to the external shield wire at the same time as the wiring in the case is facilitated, no force is applied to the conductive wires leading to both electrodes of the piezoelectric element, and the vibration of the piezoelectric element is not hindered.

When the side lengths of the bottomed case portion and the metal case portion are set so that the total length is an integral multiple of λ / 4, leakage from the bottom surface of the bottomed case portion to the side surface occurs. The phase of the emitted vibration and the phase of the vibration reflected back to the opening end of the main part of the metal case part are opposite to each other and cancel each other, thereby suppressing the vibration of the side surface of the whole case, sensitivity and output. Can be improved.

Further, when a gap between the outer jacket of the outer shield wire and each of the exposed conductors is sealed by a sealing member, the gap between the outer jacket of the outer shield wire and each of the conductors is passed through. The infiltration of moisture into the case is reliably prevented, thereby preventing the exposed electrodes and metal parts in the case from rusting and insulation failure.

Further, since a metal part is employed in a part of the case, a notch groove for drawing out the outer shield wire to the outside can be easily formed as compared with the plastic case, and the rigidity is high, so that the device can be used. Since the metal case can be directly held at the time of mounting, there is also a practical advantage that the mounting can be made robust without breaking the case.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing an ultrasonic sensor according to an embodiment of the present invention.

FIG. 2 is a schematic vertical sectional view of a case for explaining the operation of the apparatus of FIG.

FIG. 3 is a schematic longitudinal sectional view showing a configuration of a main part according to another embodiment of the present invention.

FIG. 4 is a schematic longitudinal sectional view showing a configuration of a main part according to still another embodiment of the present invention.

[Explanation of symbols]

 1: bottomed case portion 2: metal case portion having a cylindrical cross section 2a: cutout groove 3: piezoelectric element 3a: conductive layer forming an electrode 3b: conductive layer forming an electrode 4: shield member 4a: end wall 5: relay Substrate 5a: Central opening 6: Shield wire

Claims (5)

[Claims] 1. A bottomed case part made of a plastic material forming a part of the case and forming a matching layer, and a metal sealingly joined to the bottomed case part and defining a housing space for the piezoelectric element together with the bottomed case part. A piezoelectric element having electrodes on both upper and lower surfaces is attached to the inner bottom surface of the bottomed case part, and an external shield wire electrically connected to both electrodes of the piezoelectric element is formed on the metal case part. An ultrasonic sensor characterized in that it is configured to be taken out to the side of a metal case and that an open end of a metal case portion is filled with a sealing material. 2. A shield member is arranged around the piezoelectric element,
2. The ultrasonic sensor according to claim 1, wherein a relay substrate is provided at a free end of the shield member, and both electrodes of the piezoelectric element and an external shield wire are connected to relay terminals formed on the relay substrate. 3. The ultrasonic wave according to claim 1, wherein the total length of the side length of the bottomed case portion and the side length of the metal case portion is set to be an integral multiple of λ / 4. Sensors. 4. The ultrasonic sensor according to claim 1, wherein the sealing material is filled on a sponge member layer provided over the entire open end of the metal case portion. 5. The ultrasonic sensor according to claim 1, wherein a gap between the outer jacket of the outer shield wire and each conductor exposed therefrom is sealed by a sealing member.