Ultrasonic Sensor

Abstract

To provide an ultrasonic sensor which can be constituted by a smaller number of components and is not easily affected by an electromagnetic induction field.SOLUTION: In an ultrasonic sensor 1, an inner surface 3A and an outer surface 3B of a housing 3 are covered by thin film conductive layers 33, 34. A pair of engagement grooves 4 for holding a pair of opposing sides in a circuit board 13 are formed in a cylindrical main body 31 which encloses a rear space S2 of the housing 3. The pair of sides in the circuit board 13 are engaged with the pair of engagement grooves 4. A ground electrode 14 on the circuit board 13 and the thin film conductive layers 33, 34 are electrically connected.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an ultrasonic sensor used in vehicle obstacle detection devices, automatic door systems, and various other devices. [Background technology]

[0002] In Japanese Patent Laid-Open Publication No. 10-123235, a short ring made of electrically conductive metal material such as copper is fitted coaxially from the outside through a retainer to the rear part of a housing that accommodates an ultrasonic vibrator as an ultrasonic sensor in which a coil that causes a resonance phenomenon together with an ultrasonic vibrator is not affected by fluctuations in an electromagnetic induction magnetic field as an external disturbance. The axial width of this short ring is set so as to cover all components including the transformer of the processing circuit through the rear part of the housing. A circuit board on which the processing circuit is mounted is arranged in the housing so as to extend in a direction perpendicular to the center line of the housing that passes through the ultrasonic vibrator. When the electromagnetic induction magnetic field as an external disturbance existing in the vicinity of the ultrasonic sensor fluctuates, this electromagnetic induction magnetic field affects the coil of the transformer due to the fluctuation. For this reason, when the coil generates a back electromotive force due to the electromagnetic induction effect, this back electromotive force is output to the controller in a state in which it is added to the received signal as noise, and the controller erroneously detects the presence of an obstacle based on the received signal with the above noise added, even though there is no obstacle. In conventional ultrasonic sensors, a short ring is arranged via a retainer to prevent the coil that causes the resonance phenomenon together with the ultrasonic transducer from being affected by fluctuations in the electromagnetic induction magnetic field as an external disturbance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-123235 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional structure, it is necessary to attach a retainer and a short ring to the housing, which not only increases the number of parts but also increases the number of assembly steps, resulting in higher manufacturing costs. It was also found that electromagnetic induction fields act on the inside of the housing from the parts not covered by the short ring and the gap between the short ring and the outer surface of the housing, causing various noises. In addition, the conventional structure does not require the short ring to be grounded, but if it is to be grounded, it is necessary to devise a grounding structure. Another problem with the conventional structure is that it is difficult to mount and attach the circuit board.

[0005] An object of the present invention is to provide an ultrasonic sensor which can be constructed with a small number of parts and which is less susceptible to the effects of electromagnetic induction fields.

[0006] In addition to the above object, another object of the present invention is to provide an ultrasonic sensor that can be easily mounted on a circuit board. [Means for solving the problem]

[0007] The present invention is directed to an ultrasonic sensor that includes an ultrasonic transducer housed in a resin housing and a circuit board that includes a coil housed in the housing and that forms a resonant circuit with the ultrasonic transducer, and transmits ultrasonic waves by the piezoelectric effect of the ultrasonic transducer when a resonant voltage is applied to the ultrasonic transducer, and generates a reception signal through the resonant circuit by the inverse piezoelectric effect when the ultrasonic waves are reflected by an object and received by the ultrasonic transducer. In the ultrasonic sensor of the present invention, at least the inner surface of the housing is covered with a thin-film conductive layer. The thin-film conductive layer is electrically connected to a ground electrode on the circuit board. Therefore, according to the present invention, an ultrasonic sensor that is less susceptible to the effects of electromagnetic induction magnetic fields with a small number of parts can be provided. The thin-film conductive layer may be formed by using an appropriate thin-film forming technique such as plating or vapor deposition. In particular, when the thin-film conductive layer is formed as a plated layer, the variation in the thickness of the thin-film conductive layer can be controlled, and the effects of the electromagnetic induction magnetic field can be minimized, and the presence of the thin-film conductive layer can be prevented from becoming an obstacle to assembly. For example, even if the plated layer is formed by electroless nickel plating, the thickness of the plated layer can be sufficiently secured to prevent the electromagnetic induction magnetic field from acting on the inside of the housing. All of the surfaces of the housing, including the inner surface, may be covered with a thin film conductive layer. In this case, the outer surface of the housing is also covered with a plated layer, providing a double shielding effect.

[0008] Specifically, the housing may include a cylindrical main body having a cylindrical shape and an annular wall portion disposed inside the cylindrical main body and protruding inward from the cylindrical main body. In this case, the surface of the annular wall portion is also covered with a thin-film conductive layer. The ultrasonic transducer is disposed in a front space between one end of the cylindrical main body and the annular wall portion, and the circuit board is accommodated in a rear space between the other end of the cylindrical main body and the annular wall portion. With this structure, noise coming from the ultrasonic transducer side can be blocked to some extent by the annular wall portion covered with the thin-film conductive layer. The annular wall portion can also be used as a positioning means for the ultrasonic transducer and the circuit board, making it easier to assemble the ultrasonic sensor.

[0009] Furthermore, a pair of holding parts for holding a pair of opposing sides of the circuit board may be formed on the cylindrical body surrounding the rear space, and the surfaces of the pair of holding parts may also be covered with the thin-film conductive layer, and a pair of earth electrode parts electrically connected to the thin-film conductive layer covering the surfaces of the pair of holding parts may be formed along the pair of sides of the circuit board. By adopting such a structure, not only is it easy to position and fix the circuit board, but the thin-film conductive layer can be grounded reliably. If the length of the earth electrode is increased and the entire holding part is connected to the earth electrode part, the ground position of the thin-film conductive layer can be widened, and the occurrence of variations in the grounding effect due to differences in the grounding position can be prevented. The pair of holding parts can be formed from a pair of fitting grooves extending from the other end of the cylindrical body toward the annular wall part. If the pair of holding parts are formed from a pair of fitting grooves, the positioning of the circuit board can be easily performed and the circuit board can be reliably fixed, so that the occurrence of connection failure can be prevented.

[0010] A plurality of lead wires, each having a core wire connected to a plurality of connection electrodes on a circuit board, extend from an opening on the other end of the cylindrical body, and a connector terminal may be connected to the core wires of the plurality of lead wires. Providing a connector terminal via the plurality of lead wires increases the degree of freedom in the installation position of the ultrasonic sensor.

[0011] Furthermore, if the rear space is sealed with molded resin, the waterproof performance can be easily improved. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a perspective view of the ultrasonic sensor according to the embodiment in a vertical position. [Diagram 2] 2 is a cross-sectional view taken along line II-II in FIG. 1, in which the internal structure of the ultrasonic transducer and the molding resin are omitted. [Diagram 3] 1A and 1B are schematic diagrams showing the covering structure of a housing. [Figure 4] 1 is a perspective view of an ultrasonic sensor according to an embodiment of the present invention, as viewed from a connector terminal side. [Diagram 5]FIG. 2 is an end view of line VV in FIG. [Figure 6] FIG. 2 is a bottom view of the ultrasonic sensor in the state shown in FIG. [Figure 7A] FIG. 13 is a diagram showing an example of an output of an ultrasonic sensor when a plating process is performed. [Figure 7B] FIG. 13 is a diagram showing an example of an output from an ultrasonic sensor when no plating process is performed. [Figure 8A] FIG. 13 is a diagram showing an example of an output from an ultrasonic sensor when a plating process is performed (when an object to be measured is present); [Figure 8B] FIG. 13 is a diagram showing an example of the output of the ultrasonic sensor when no plating process is performed (when an object to be measured is present). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of an ultrasonic sensor according to the present invention will be described with reference to the drawings.

[0014] FIG. 1 is a perspective view of an ultrasonic sensor 1 according to the present embodiment, which can be used in an obstacle detection device that functions as a corner sonar for a vehicle, in a vertical position. However, the molding resin inside the housing 3 is omitted in FIG. 1. FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1, omitting the illustration of the structure inside the ultrasonic transducer 5 and the molding resin. Note that hatching showing the cross-sectional portion is omitted in FIG. 2. FIGS. 3(A) and 3(B) are schematic diagrams showing the covering structure of the housing 3. FIG. 4 is a perspective view of the ultrasonic sensor 1 according to the present embodiment, as seen from the connector terminal 7 side. FIG. 5 is an end view taken along line VV in FIG. 1, and FIG. 6 is a bottom view in the state shown in FIG. 1.

[0015] A connector terminal 7 is connected to this ultrasonic sensor 1 via three lead wires 9. The three lead wires 9 are soldered to connection electrodes included in a circuit pattern of a circuit board 13 housed inside the housing 3.

[0016] The ultrasonic sensor 1 is attached to, for example, the front bumper of a vehicle when in use. The ultrasonic sensor 1 includes a housing 3 formed of an insulating resin material such as a PBT resin material. The housing 3 includes a cylindrical main body 31 having a cylindrical shape, and an annular wall portion 32 disposed inside the cylindrical main body 31 and protruding inward from the cylindrical main body 31. An ultrasonic transducer 5 is disposed in a front space S1 between a tip end (one end) of the cylindrical main body 31 and the annular wall portion 32, and a circuit board 13 is housed in a rear space S2 between a rear end (the other end) of the cylindrical main body 31 and the annular wall portion 32.

[0017] As shown in FIG. 3(A), in the ultrasonic sensor 1 of this embodiment, the inner surface 3A and the outer surface 3B of the housing 3 are covered with thin-film conductive layers 33 and 34. The thin-film conductive layers 33 and 34 may be formed using an appropriate thin-film forming technique such as plating or vapor deposition. In this embodiment, the entire inner surface 3A and the entire outer surface 3B of the housing 3 are covered with one or more plating layers such as electroless nickel plating. A preferred plating layer is made of electroless nickel plating or the like, and is a plating layer that blocks electrolytic noise and magnetic noise. The plating layer is thick enough to prevent the electromagnetic induction magnetic field from acting on the inside of the housing 3.

[0018] The thin-film conductive layers 33 and 34 are electrically connected to a ground electrode on the circuit board 13, which will be described later. If the thin-film conductive layers 33 and 34 are formed of plated layers, the variation in thickness of the thin-film conductive layers can be controlled, the influence of the electromagnetic induction magnetic field can be minimized, and the presence of the thin-film conductive layers can be prevented from interfering with assembly. In particular, if the outer surface 3B of the housing 3 is also covered with a plated layer as in this embodiment, a double shielding effect can be achieved. Furthermore, with such a structure, the noise coming from the ultrasonic transducer 5 side can be blocked to some extent by the annular wall portion 32 covered with the thin-film conductive layer 33. Furthermore, the annular wall portion 32 can also be used as a positioning means for the ultrasonic transducer 5 and the circuit board 13, making the assembly of the ultrasonic sensor easier.

[0019] In this embodiment, a pair of fitting grooves 4 are formed in the cylindrical body 31 surrounding the rear space S2 as a pair of holding parts for holding a pair of opposing sides of the circuit board 13. As shown in FIG. 3B, the inner surfaces of the pair of fitting grooves 4 are also covered with a thin-film conductive layer 33. A pair of earth electrodes 14 are formed along a pair of sides of the circuit board 13 and are electrically connected to the thin-film conductive layer 33 covering the surfaces of the pair of fitting grooves 4. In this embodiment, the earth electrodes 14 are formed along the sides on the front and back surfaces of the circuit board 13 in the thickness direction. The present invention can also be realized by forming one earth electrode 14 along one side of the circuit board on one of the front and back surfaces of the circuit board 13 in the thickness direction. The electrical connection between the thin-film conductive layer 33 covering the surfaces of the pair of fitting grooves 4 and the earth electrode 14 may be realized by strong contact, but it is preferable to join them using solder or a conductive adhesive. When solder is used, solder cream is applied to the earth electrode 14, and after the circuit board 13 is fitted into the pair of fitting grooves 4, the entire structure is heated to melt the solder cream. By adopting such a structure, not only is it easy to position and fix the circuit board 13, but it also ensures that the thin-film conductive layer 33 is grounded. If the length of the earth electrode 14 is increased and the entire fitting groove 4 is connected to the earth electrode 14, the ground position of the thin-film conductive layer 33 can be widened, and variations in the grounding effect due to differences in the grounding position can be prevented.

[0020] Although not shown, the circuit board 13 is molded in the rear space S2 of the housing 3 with a moisture-proof silicone resin (not shown). On the other hand, the ultrasonic transducer 5 is coaxially molded in the front space S1 of the housing 3 with a vibration-absorbing elastic resin such as silicone rubber.

[0021] Here, the ultrasonic transducer 5 is a commercially available product that is configured by bonding a piezoelectric element inside an aluminum casing with an epoxy adhesive. If the entire inner and outer surfaces of the housing 3 are covered with a thin conductive layer as in this embodiment, the highest sealing effect can be provided for the components placed inside the housing, so even if an ultrasonic transducer 5 that has not been provided with special noise countermeasures is used, the performance as an ultrasonic sensor is not significantly affected.

[0022] The ultrasonic transducer 5 is connected to a resonant circuit on a circuit board 13 via a wire harness 15. A transformer 16 including a capacitor 19 and a coil constituting a resonant circuit, an IC 18 for signal processing, and the like are mounted on the circuit board 13. The secondary coil of the transformer 16 is used as a coil as a component constituting the resonant circuit. In this embodiment, the signal processing circuit including the resonant circuit and the amplifier circuit mounted on the circuit board 13 adopts a known configuration.

[0023] A piezoelectric element (not shown) in the ultrasonic transducer 5 exerts a piezoelectric effect and an inverse piezoelectric effect, and this piezoelectric element is connected to the secondary coil of the transformer 16 via the wire harness 15. A parallel resonant circuit is formed including the piezoelectric element in the ultrasonic transducer 5, the capacitor 19, and the secondary coil of the transformer 16. When a drive voltage is applied to the primary coil of the transformer 16 under the control of the IC 18, the transformer 16 boosts the drive voltage, and the boosted drive voltage is generated in the secondary coil. Accordingly, mechanical vibration is generated by the piezoelectric effect of the piezoelectric element in the ultrasonic transducer 5. As a result, the ultrasonic transducer 5 transmits ultrasonic waves forward from its transmission / reception surface 51 through the opening 35 of the housing 3. When the transmitted ultrasonic waves are reflected by an obstacle located in front, the ultrasonic transducer 5 receives the reflected ultrasonic waves at its transmission / reception surface 51 and transmits them to the piezoelectric element. Therefore, the piezoelectric element generates a piezoelectric voltage due to the inverse piezoelectric effect, and outputs this piezoelectric voltage to the amplifier circuit through the parallel resonant circuit.

[0024] In the above embodiment, the inner and outer surfaces of the housing 3 are all covered with a thin-film conductive layer consisting of a plated layer. Although it is possible to obtain the effects of the invention by covering at least the inner surface of the housing 3 with a thin-film conductive layer, from the viewpoint of plating workability, it is preferable to cover the inner and outer surfaces of the housing in their entirety with a plated layer.

[0025] FIG. 7(A) is a diagram showing an example of the output of the ultrasonic sensor when the ultrasonic sensor of the present embodiment, in which the cylindrical body 31 is plated, is wrapped in a towel so as not to receive reflected waves, and a noise source is placed at a position 30 cm away. FIG. 7(B) is a diagram showing an example of the output of the ultrasonic sensor when the ultrasonic sensor of the comparative example, in which the cylindrical body 31 is not plated, is wrapped in a towel so as not to receive reflected waves, and a noise source is placed at a position 30 cm away. In FIGS. 7(A) and (B), the horizontal axis is the distance (mm) from the ultrasonic sensor, and the vertical axis is the strength of the received radio wave. In FIGS. 7(A) and (B), the large signal appearing near the distance 0 to near the distance 200 mm is the transmission signal of the ultrasonic sensor. The reason why the strength of the received radio wave from a position far away is large is because the amplification factor of the IC used is set to increase in proportion to the distance. This is also true in FIG. 7(B). The received signals N and N' in FIGS. 7(A) and (B) correspond to the noise detected by the ultrasonic sensor. Comparing the signals N and N' in FIGS. 7(A) and (B), the noise peak of the ultrasonic sensor of this embodiment is significantly smaller for the same noise source.

[0026] FIG. 8(A) is a diagram showing an example of the output S of the ultrasonic sensor when a measurement target is placed at multiple positions in front of the ultrasonic sensor of the present embodiment, in which the cylindrical body 31 is plated. FIG. 8(B) is a diagram showing an example of the output S' of the ultrasonic sensor when a measurement target is placed in front of an ultrasonic sensor of a comparative example, in which the cylindrical body 31 is not plated, under the same conditions. S1 in FIG. 8(A) is a signal reflected from the measurement target located closest to the ultrasonic sensor. The signal S'1 in FIG. 8(B) is also a signal reflected from the measurement target located closest to the ultrasonic sensor, but has a higher peak value than the signal S1 in FIG. 8(A). This is because noise is included. The peak value of the signal at the far position in FIG. 8(A) is also high. This is because noise is included. Also, as can be seen by comparing the multiple signals Sd at the far position in Fig. 8(A) with the signal S'd at the far position in Fig. 8(B), the number of signals in the signal S'd at the far position in Fig. 8(B) is large, and there is no difference in the crest value of each signal, making it unclear which signal is the correct detection signal. From the comparison of Figs. 8(A) and (B), it can be seen that the ultrasonic sensor of the embodiment of the present invention is less susceptible to the influence of noise and can correctly detect the presence of a measured object. [Industrial Applicability]

[0027] According to the present invention, it is possible to provide an ultrasonic sensor which has a small number of parts and is less susceptible to the effects of electromagnetic induction magnetic fields. [Explanation of symbols]

[0028] 1 Ultrasonic sensor 3. Housing 3A Inner surface 3B External surface 31 Cylindrical body 32 Annular wall 33,34 Thin film conductive layer 35 Opening 4 Fitting groove (retaining part) 5 Ultrasonic transducer 7 Connector terminal 9 Lead Wire 13 Circuit Board 14 Earth electrode part 15 Wire Harness 16 Transformer 18 IC 19 Capacitor S1 Front space S2 Rear Space

Claims

1. An ultrasonic sensor comprising an ultrasonic transducer housed in a resin housing, and a circuit board having a coil housed in the housing and constituting a resonant circuit with the ultrasonic transducer, wherein when a resonant voltage is applied to the ultrasonic transducer, an ultrasonic sensor transmits an ultrasonic wave by a piezoelectric effect of the ultrasonic transducer, and when the ultrasonic wave is reflected by an object and received by the ultrasonic transducer, a reception signal is generated through the resonant circuit by an inverse piezoelectric effect, At least the inner surface of the housing is covered with a thin conductive layer; 4. An ultrasonic sensor comprising: a thin-film conductive layer electrically connected to a ground electrode on the circuit board;

2. 2. The ultrasonic sensor according to claim 1, wherein all of the surfaces of the housing, including the inner surface, are covered with the thin-film conductive layer.

3. The housing includes a cylindrical main body having a cylindrical shape and an annular wall portion disposed inside the cylindrical main body and protruding inward from the cylindrical main body, the surface of the annular wall portion is also covered with the thin-film conductive layer; The ultrasonic transducer is disposed in a front space between one end of the cylindrical body and the annular wall portion, 3. The ultrasonic sensor according to claim 1, wherein the circuit board is accommodated in a rear space between the other end of the cylindrical body and the annular wall portion.

4. a pair of holding portions for holding a pair of opposing sides of the circuit board are formed on the cylindrical main body surrounding the rear space, The surfaces of the pair of holding parts are also covered with the thin film conductive layer, 4. The ultrasonic sensor according to claim 3, further comprising a pair of earth electrodes formed along the pair of sides of the circuit board, the pair of earth electrodes being electrically connected to the thin-film conductive layer covering the surfaces of the pair of holding portions.

5. The ultrasonic sensor according to claim 4 , wherein the pair of holding portions are formed of a pair of fitting grooves extending from the other end of the cylindrical body toward the annular wall portion.

6. 4. The ultrasonic sensor according to claim 3, wherein a plurality of lead wires each having a core wire connected to a plurality of connection electrodes on the circuit board extend from an opening on the other end of the cylindrical body, and connector terminals are connected to the core wires of the plurality of lead wires.

7. 4. The ultrasonic sensor according to claim 3, wherein the rear space is sealed with a molding resin.

8. 2. The ultrasonic sensor according to claim 1, wherein the thin-film conductive layer is a plated layer.

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