Method for producing a transducer device for a vibration sensor, transducer device, and vibration sensor

Abstract

The invention relates to a method for producing a transducer device (2) for a vibration sensor. A contacting electrode (8) is etched and covered with an adhesive agent (10) and a contact material (11). The contacting electrode (8) is inserted between two piezo elements (7), and the piezo elements (7) and the contacting electrode (8) are connected to one another.

Description

[0001] Method for manufacturing a transducer device for a vibration sensor, as well as transducer device and vibration sensor

[0002] The invention relates to a method for manufacturing a transducer device for a vibration sensor. The invention further relates to a correspondingly manufactured transducer device and a vibration sensor with such a transducer device.

[0003] Vibration sensors are known in the art, for example, in the form of tuning forks or single rods. Such sensors have a mechanically vibrating unit that is excited to mechanical vibrations by a drive-receiver unit. The vibrations resulting from the interaction with a medium to be measured or monitored are received by the drive-receiver unit and processed. For measurement purposes, it is used, for example, that the vibration frequency or amplitude changes when the mechanically vibrating unit transitions from an uncovered to a state covered by the medium. This allows, for example, the monitoring of the fill level of the medium in a container.

[0004] The drive-receiver unit typically contains a transducer device that converts between electrical signals and mechanical vibrations. Piezoelectric elements are often used for this purpose. These elements have a polarized ceramic surface and at least one electrode on one end face for electrical contact. To increase the generated mechanical force, it is known to arrange several piezoelectric elements in a stack. For electrical contact, a contact electrode, also known as a solder or weld tab, is located between two piezoelectric elements and thus also in electrical connection with the electrodes of the piezoelectric elements.

[0005] Since the contact electrode is made of a metal, usually stainless steel, and the piezoelectric elements are made of a ceramic, achieving a reliable connection over an extended period can be very complex. This is especially true if a wider temperature range (e.g., between -50 °C and +250 °C) is required. With ceramic contact electrodes, it is particularly likely that the end faces will not be perfectly flat or perfectly parallel to each other.

[0006] Methods for producing piezo stacks are disclosed, for example, in DE 689 19 556 T2, JP S62 - 165 381 A, US 5,271 , 133 A or DE 10 2020 125 707 A1 .

[0007] The invention is based on the objective of improving the connection between a contacting electrode and the adjacent piezoelectric elements.

[0008] The problem is solved by a method for manufacturing a transducer device for a vibration sensor, wherein the transducer device comprises several piezoelectric elements, each with at least one electrode and at least one - preferably made of stainless steel, e.g. 1 .4016 existing - contact electrode, wherein the method comprises at least the following steps: that at least a part of a surface of the contact electrode is preferably electrochemically - at least partially etched, that the etched part of the surface of the contact electrode is at least partially covered with a first material - preferably gold and / or nickel and / or silver - as an adhesion promoter, that the part of the surface of the contact electrode covered with the adhesion promoter is at least partially covered with a second material - preferably silver - as a contact material, that the contact electrode is inserted between two piezoelectric elements, and that the two piezoelectric elements and the contact electrode are connected to each other - preferably by a combined application of pressure and temperature.

[0009] In one embodiment, the contact electrode has a base located between the piezoelectric elements and a contact tab protruding from the stack formed by the piezoelectric elements. The contact electrode is preferably made of stainless steel. The Young's modulus of stainless steel is between 190 GPa and 210 GPa. Etching the surface removes, for example, an oxide layer on the contact electrode that would otherwise prevent a good bond between the material – e.g., stainless steel – of the contact electrode and the ceramic of the piezoelectric element, or between the contact electrode and the layer to be coated.

[0010] In one embodiment, electrochemical etching is performed. In a further embodiment, etching takes place with hydrochloric acid (HCl) or sulfuric acid (H₂SO₄). During etching, in one embodiment, the object to be treated, i.e., the contact electrode, is connected to the negative terminal of a voltage source. This is intended to prevent the hydrogen that forms at the positive terminal of the aforementioned voltage source from potentially causing embrittlement of the contact electrode, e.g., made of stainless steel. In one embodiment, the contact electrode consists of a ferrous alloy.

[0011] In one embodiment, the adhesion promoter and / or the contact material are applied electroplated.

[0012] The first and / or the second material are preferably selected in such a way that they have a lower Young's modulus than the contact electrode. This is intended to ensure that the coating formed from the two materials is more compliant than the contact electrode itself. Therefore, it conforms more closely to the surfaces of the piezoelectric elements.

[0013] One embodiment involves treating the contact electrode so that at least the portion of its surface that is at least partially etched is essentially free of oil and grease. This step is performed before the surface etching. Removing oil or grease layers as a pretreatment significantly improves the results of the subsequent coating process.

[0014] According to the aforementioned embodiment, the method thus comprises the following steps: treating the contacting electrode such that at least part of its surface is substantially free of oil and grease; etching at least part of the oil- and grease-free part of the contacting electrode's surface – preferably electrochemically; covering at least part of the etched part of the contacting electrode's surface with a first material – preferably gold and / or nickel and / or silver – as an adhesion promoter; covering at least part of the contacting electrode's surface with the adhesion promoter with a second material – preferably silver – as a contact material; and inserting the contacting electrode between two piezoelectric elements.and that the two piezoelectric elements and the contacting electrode are connected to each other - preferably by a combined application of pressure and temperature.

[0015] According to one embodiment, the adhesion promoter and the contact material are applied to two sides of the contacting electrode. In this embodiment, a coating is applied to both the top and bottom surfaces of the contacting electrode.

[0016] One embodiment provides that at least on the sides of the two piezo elements, between which the contacting electrode is located, an electrode is applied by means of sputtering.

[0017] One embodiment involves connecting the two piezoelectric elements through the application of force and temperature. In this embodiment, the piezoelectric elements and the contact electrode are thus fused together.

[0018] In a supplementary embodiment, the first material is gold, whose modulus of elasticity is approximately 78 GPa.

[0019] In a further supplementary or alternative embodiment, the second material is silver with a Young's modulus between 80 GPa and 100 GPa. One embodiment relates that the two piezoelectric elements—and preferably all piezoelectric elements of the transducer device—have essentially the same material properties and / or the same dimensions. In a supplementary embodiment, the piezoelectric elements are each disks or flat rings, made of the same ceramic, and preferably polarized from one end face to the other.

[0020] One embodiment involves cutting the two piezoelectric elements from a cylindrical roll. This method of manufacturing piezoelectric elements is known in the prior art and is very efficient and cost-effective. A disadvantage, however, is that the cutting process can create grooves in the piezoelectric elements. The method according to the invention helps to compensate for these grooves.

[0021] One embodiment provides that the first material and / or the second material is selected such that it has a strength that is closer to that of the piezoelectric elements than to that of the contact electrode. This embodiment aims to ensure that the coating's strength is more similar to that of the ceramic material of the piezoelectric elements than to that of the contact electrode material. The Young's modulus of a ceramic, for example, lies between 50 GPa and 60 GPa.

[0022] A further supplementary or alternative embodiment involves selecting the first and / or second material such that it has a hardness lower than that of the piezoelectric elements and the contact electrode. In this embodiment, the coating is preferably significantly softer than both the piezoelectric elements and the contact electrode. For example, the hardness values ​​in one embodiment are approximately 75 HV for silver, approximately 200 HV for stainless steel 1.4016, approximately 140 HV for gold, and approximately 1000 HV for the ceramic from which the piezoelectric elements are made. The soft coating allows for the compensation of unevenness or slightly non-parallel surfaces. Furthermore, the coating creates a stiffness gradient, thus reducing mechanical stress between the ceramic material combination and, for example, the stainless steel of the contact electrode at elevated temperatures.

[0023] The invention further relates to a transducer device for a vibration sensor, which has been manufactured using the method according to one of the preceding or following embodiments. The embodiments and explanations apply accordingly to the transducer device, so repetition is unnecessary.

[0024] Furthermore, the invention relates to a vibration sensor comprising a mechanically oscillating unit and a transducer device, wherein the transducer device excites the mechanically oscillating unit to mechanical vibrations and receives mechanical vibrations from the mechanically oscillating unit, and wherein the transducer device is manufactured using the method according to one of the preceding or following embodiments. The embodiments and explanations apply accordingly to the vibration sensor, so repetition is omitted.

[0025] The invention is explained in more detail with reference to the following figures.

[0026] Fig. 1 shows a schematic cross-sectional view of a vibration sensor.

[0027] Fig. 2 shows a spatial representation of one side of a piezoelectric element and

[0028] Fig. 3 shows a schematic section through a coated contact electrode.

[0029] Figure 1 shows a so-called vibrating fork as an example of a vibration sensor design. The mechanically vibrating unit 1 has two fork prongs connected to a diaphragm 4. On the opposite, and therefore inner, side of the diaphragm 4, a transducer device 2 is located in a housing 3 (indicated here). This transducer device has several disc-shaped piezoelectric elements 7 arranged in a stack. For example, a contact electrode 8 (also called a solder or weld tab) is located between two piezoelectric elements 7. This electrode protrudes from the stack and serves for electrical contact. The transducer device 2 is pressed against the diaphragm 4 by a pressure screw 5 via a hemispherical intermediate element 6.

[0030] Figure 2 shows a disc-shaped piezoelectric element 7 with a double reversal contact. This means that the two electrodes 9, located on opposite sides of the piezoelectric element 7, are each guided across the outer surface to the opposite side. The semicircular area below the depicted electrode 9 therefore belongs to the electrode 9 on the underside (not shown). Furthermore, it can be seen that the electrode 9 is guided across the underside via the indentation shown here at the top.

[0031] Figure 3 shows the coating on both sides of the contact electrode 8, which is made of, for example, stainless steel. On the surface, which has been cleaned of oil and grease and etched, there is an adhesion promoter 10, which is, for example, a gold layer. On top of this is a contact material 11, which is, for example, silver and serves to connect the contact electrode 8 to the piezoelectric element 7. The part of the contact electrode 8 on the right side is the contact tab. In an alternative version – not shown – there is a nickel layer between the contact electrode and the gold layer.

[0032] Reference symbol for mechanically oscillating unit

[0033] Converter device

[0034] Housing

[0035] membrane

[0036] pressure screw

[0037] Intermediate element

[0038] Piezoelectric element

[0039] Contact electrode

[0040] electrode

[0041] Liability mediator

[0042] Contact material

Claims

Patent claims 1. Method for manufacturing a converter device (2) for a Vibration sensor, wherein the transducer device (2) comprises several piezo elements (7) each with at least one electrode (9) and at least one - preferably made of stainless steel, e.g. 1.4016 existing - contact electrode (8), wherein the method comprises at least the following steps: that at least a part of a surface of the contact electrode (8) is at least partially etched - preferably electrochemically, that the etched part of the surface of the contact electrode (8) is at least partially covered with a first material - preferably gold and / or nickel and / or silver - as an adhesion promoter (10), that the part of the surface of the contact electrode (8) covered with the adhesion promoter (10) is at least partially covered with a second material - preferably silver - as a contact material (11), that the contact electrode (8) is inserted between two piezoelectric elements (7), and that the two piezoelectric elements (7) and the contact electrode (8) are connected to each other - preferably by a combined application of pressure and temperature.

2. The method according to claim 1, wherein the contacting electrode (8) is treated such that at least the part of the surface of the contacting electrode (8) which is at least partially etched is substantially free of oil and grease.

3. Method according to claim 1 or 2, wherein the adhesion promoter (10) and the contact material (11) are applied to two sides of the contacting electrode (8).

4. Method according to one of claims 1 to 3, wherein the two piezo elements (7) are connected to each other by the action of force and temperature.

5. Method according to any one of claims 1 to 4, wherein the two piezo elements (7) are cut from a cylindrical roll.

6. Method according to any one of claims 1 to 5, wherein the first material and / or the second material is selected such that the first material and / or the second material has a smaller modulus of elasticity than the contacting electrode (8).

7. Method according to any one of claims 1 to 6, wherein the first material and / or the second material is selected such that the first material and / or the second material has a strength which is closer to the strength of the piezoelectric elements (7) than to the strength of the contacting electrode (8).

8. Method according to any one of claims 1 to 7, wherein the first material and / or the second material is selected such that the first material and / or the second material has a hardness which is less than the hardness of the piezoelectric elements (7) and less than the hardness of the contacting electrode (91).

9. Converter device (2) for a vibration sensor, wherein the converter device (2) has been manufactured using the method according to any one of claims 1 to 8.

10. Vibration sensor, comprising a mechanically oscillating unit (1 ) and a transducer device (2), wherein the transducer device (2) excites the mechanically oscillating unit (1 ) to mechanical vibrations and receives mechanical vibrations from the mechanically oscillating unit (1 ), and wherein the transducer device (2) has been manufactured according to the method of any one of claims 1 to 8.

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