Method for producing a transducer device and vibration sensor

Abstract

The invention discloses a method for producing a transducer device (1). Two polarized piezo elements (2) are arranged relative to one another such that one end face (20, 21) of the piezo elements (2) is in contact with one another and an electrode (23, 24) of the piezo elements (2) is located between them. While mechanical pressure is exerted on the piezo elements (2), the piezo elements (2) are bonded to one another by the action of thermal energy over a predetermined period of time at a maximum temperature below a Curie temperature of the at least two piezo elements (2). The invention further relates to a vibration sensor having a transducer device (1).

Description

[0001] The invention relates to a method for manufacturing a transducer device. Furthermore, the invention relates to a vibration sensor. The vibration sensor serves, for example, to determine and / or monitor a process variable of a medium. The process variable is, for example, the fill level, and the medium is, for example, a liquid, a gas, or a bulk material.

[0002] Vibration sensors are known in the art that have a mechanically oscillating unit that is excited to mechanical vibrations by a drive / receiver unit. The vibrations resulting from the interaction with a medium are received and evaluated by the drive / receiver unit. For example, a measurement exploits the fact that the vibration frequency or amplitude changes when the mechanically oscillating unit transitions from an uncovered state to a state covered by the medium. This allows, for example, the monitoring of the fill level of the medium in a container.

[0003] The drive / receiver unit typically contains a converter device that converts between electrical signals and mechanical vibrations. Piezoelectric elements are often used for this purpose. These elements feature a polarized ceramic and at least one electrode applied to one end face for electrical contact. If the mechanical force to be generated is to be increased, it is common practice to arrange several piezoelectric elements in a stack. For electrical contact, it is then necessary to contact all the elements individually or at least with each other. This is very complex and costly.

[0004] EP 1 277 243 B1 discloses a method for manufacturing a transducer device from piezoelectric elements. After grooves for contact lines have been introduced, the piezoelectric elements are glued together and bonded by diffusion welding at a temperature above their Curie temperature. Subsequently, polarization of the entire stack is achieved.

[0005] During polarization, residual strains can occur in the piezo element due to the alignment of the dipoles. During manufacturing, care must also be taken to ensure that no air gap develops between the individual piezo elements.

[0006] The invention is based on the object of proposing a method for producing a transducer device - preferably for a vibration sensor - which creates the best possible connection between individual piezo elements.

[0007] The object is achieved by a method for producing a transducer device, wherein the transducer device generates mechanical vibrations and / or receives mechanical vibrations, wherein the method comprises at least the following steps: that at least two at least partially polarized piezo elements are arranged relative to each other in such a way that one end face of the piezo elements is in contact with each other and at least one electrode of the piezo elements is located between the end faces, that - preferably perpendicular to the front sides - a mechanical pressure is exerted on the at least two piezo elements, and that the at least two piezo elements, while the mechanical pressure is exerted on them, are connected to one another - in particular baked together - by the action of thermal energy over a predetermined period of time with a maximum temperature below a Curie temperature of the at least two piezo elements.

[0008] The resulting transducer device can alternatively be referred to as a piezoelectric transducer device, as it consists of at least two piezoelectric elements. It is preferably used in a vibration sensor for transmitting and / or receiving mechanical vibrations or for converting between electrical signals and mechanical vibrations.

[0009] In the method according to the invention, at least two piezo elements that are at least partially polarized are stacked on top of each other and bonded together using thermal energy—e.g., in a furnace. While the piezo elements are heated, mechanical pressure is exerted on them.

[0010] The at least two piezo elements each have end faces that are first brought into contact with each other and then bonded together by thermal energy. At least one piezo element has at least one electrode on its end face. The electrode serves to either apply an electrical excitation signal to the piezo element and / or to pick up an electrical reception signal from the piezo element.

[0011] Preferably, each piezo element has one or even two electrodes. The electrodes of a piezo element are each assigned a different polarization (i.e., positive pole and negative pole). Their arrangement depends on the polarization pattern within the piezo element. During the manufacturing process, at least one electrode of a piezo element is located between the contacting end faces.

[0012] The mechanical pressure is preferably applied perpendicular to the end faces. This applies in particular to the case where the transducer device, e.g., in a vibration sensor, is arranged such that the piezo elements receive or generate mechanical vibrations perpendicular to their end faces.

[0013] The temperature associated with the applied thermal energy is below the Curie temperature of the piezo elements. In one embodiment, the piezo elements are made of the same material and therefore have the same Curie temperature. If the piezo elements have different Curie temperatures, the maximum temperature acting on the piezo elements is lower than the minimum Curie temperature of the piezo elements. By keeping the temperatures lower than the Curie temperature, depolarization of the piezo elements is avoided. Furthermore, aging of the piezo elements is achieved, which stabilizes their properties during use.

[0014] In one embodiment, a pressure between 10 MPa and 20 MPa is applied. The bonding is achieved by subjecting the piezo elements to a temperature between 200 °C and 300 °C for several hours in an oven. The diameter of a piezo element is in one embodiment in the range between 5 and 15 mm.

[0015] One embodiment of the process provides for a space between the contacting end faces to be kept free of adhesive during the process. In this embodiment, the piezo elements are stacked on top of each other without adhesive, thus ensuring a dry stack. This prevents any material from evaporating between the end faces during the heating process. Any remaining adhesive residue would also have a dampening effect.

[0016] One embodiment of the method involves connecting the two piezo elements to one another by interconnecting electrodes located between the two piezo elements. Material preferably diffuses from one electrode to the other electrode and vice versa. Since the electrodes are directly and inseparably connected to the piezo elements, the piezo elements are also connected to one another. In this embodiment, at least one electrode between the end faces consists at least partially or entirely of silver or a silver-containing material. Furthermore, during the method, temperatures and pressures are preferably exerted on the piezo elements to be connected such that diffusion occurs between the electrodes.

[0017] One embodiment of the method provides for the two piezo elements to be arranged relative to one another such that a contacting electrode is located between them. Electrical signals can be transmitted to the transducer device or electrical signals can be conducted away from it via a contacting electrode (another term is, for example, a soldering tag). The contacting electrode thus establishes the electrical connection to the electrode. In this embodiment, the contacting electrode is connected to the transducer device, while the at least two piezo elements are connected to one another. This simplifies the manufacturing and handling of the components.

[0018] In one embodiment, a contacting electrode is connected to a face of one piezo element during the connection of the piezo elements to one another, which is opposite the face that is in contact with the face of the other piezo element. This contacting electrode is thus mounted above or below the stack of at least two piezo elements.

[0019] One embodiment of the method involves producing the piezo elements in such a way that the piezo elements each have two end faces and an outer casing, that an electrode is applied to each end face, and that each electrode is guided from one end face of the two end faces over the outer casing to the other end face of the two end faces. The piezo elements each have two end faces and an outer casing. On each end face there is an electrode for electrical contact. In addition, each electrode is guided over the outer casing of the piezo element to the other end face. This means that there are two electrodes on each end face, which are preferably electrically insulated from one another. The electrodes themselves extend from one end face over the outer casing to the other end face. This has the advantage that both sides of the piezo element can be contacted via each end face.It's not necessary to connect a single contact to each end face; it's sufficient to connect two contacts to one end face. This significantly simplifies the contacting effort.

[0020] Furthermore, it becomes easier to arrange multiple piezo elements in a stack and connect them electrically. Therefore, one design provides for the piezo elements to be arranged relative to one another in such a way that the respective electrodes face each other and are thus directly connected during production.

[0021] One embodiment of the method provides for the piezo elements to be at least partially polarized before or after the electrode is applied. In one embodiment, at least one electrode—or two electrodes—are first applied to the piezo elements (e.g., by firing at a temperature above the Curie temperature of the electrode(s). The polarization is then generated.

[0022] In one embodiment, a piezo element with at least or exactly one recess in an outer casing is used. The piezo element preferably has a substantially circular cross-section. The recess, as a deviation from this or another symmetrical shape, assists in positioning the piezo elements relative to one another and / or in installing the transducer device, e.g., in the vibration sensor. The correct orientation is relevant, for example, to create an overlap between the superimposed electrodes of the individual piezo elements. The recess thus serves as an aid for the assembly and orientation of the components of the transducer device. Preferably, all piezo elements have a recess.

[0023] One embodiment of the method involves polarizing the piezo elements in such a way that one polarization is perpendicular to the end faces of the piezo elements. In this embodiment, the polarization runs from one end face to the other, resulting in the positive pole on one side and the negative pole on the other.

[0024] One embodiment of the method provides for the piezo elements to be produced as essentially circular disks. The disks have an essentially circular cross-section. In one embodiment, at least one deviation from the circular shape is present, which, for example, simplifies the orientation of the piezo elements during production.

[0025] One embodiment of the method involves arranging and connecting an odd number of piezo elements. The piezo elements are preferably stacked on top of each other so that electrodes of the same polarity touch each other, meaning that the polarization of the piezo elements is always opposite. In one embodiment, three or five piezo elements are used.

[0026] One embodiment of the method provides that the maximum temperature is specified depending on an application temperature range specified for the transducer device. This embodiment takes advantage of the fact that the piezo elements are already exposed to higher temperatures during production, resulting in preconditioning under compressive load and higher temperatures. Therefore, during subsequent use of the transducer device, for example, settlement effects or depolarization are not possible or only occur to a significantly reduced extent. The pre-aged piezo elements therefore have essentially unchanging properties. This prevents, in particular, the effect of amplitude losses due to depolarization as a result of preload and temperature influences in the installed state during use.

[0027] In one embodiment, a preferably through-hole is introduced into the stack of piezo elements. In another embodiment, at least some of the piezo elements are rings.

[0028] One embodiment of the method includes the method being part of a method for manufacturing a vibration sensor. In this embodiment, the method for manufacturing the transducer device is a part or a block of the method for manufacturing a vibration sensor in which the transducer device is installed. Thus, it can also be formulated conversely that the invention relates to a method for manufacturing a vibration sensor in which the transducer device is manufactured according to one of the preceding or following embodiments.

[0029] The invention further relates to a vibration sensor with a mechanically oscillatable unit and with a transducer device, wherein the transducer device excites the mechanically oscillatable unit to mechanical vibrations and / or receives mechanical vibrations from the mechanically oscillatable unit, and wherein the transducer device is manufactured using the method according to one of the preceding or following embodiments. The mechanically oscillatable unit is, for example, a tuning fork, a single rod, or a membrane.

[0030] The explanations and descriptions of the procedure also apply to the vibration sensor, so there is no need to repeat them.

[0031] The invention is explained in more detail with reference to the following figures. Fig. 1 shows a front side of a piezo element, Fig. 2 shows the other end face of the piezo element of the Fig. 1, Fig. 3 shows a stack of piezo elements and Fig. Figure 4 shows schematically the structure of a vibration sensor with a transducer device.

[0032] The Fig. 1 and Fig. 2 shows the two end faces 20, 21 of an exemplary piezo element 2.

[0033] On each of the end faces 20, 21, there is a largely circular electrode 23, 24, preferably made of silver or a silver mixture. The electrodes 23, 24 are partially adjacent to the edge of the end face 20, 21, in order to be guided along the outer jacket 22 to the opposite end face 21, 20. On the respective opposite end face 21, 20, the electrode 23, 24 has a smaller extension. The electrodes 23, 24 are designed such that on each end face 20, 21, the two sections for the respective non-contacting from one end face 21, 20 to the other are opposite one another.

[0034] In the Fig. 3, the course of an electrode 24 can be seen on the outer shells 22 of the piezo elements 2 of the transducer device 1, which causes a re-contact.

[0035] The insulation disks 11 as the upper and lower ends of the stack, respectively, as well as the insulation disk 11 in the stack, result in a total of two separate stacks of piezo elements 2, which serve separately to excite and receive the mechanical vibrations. Four contacting electrodes 8 are sufficient for this. The shape of the contacting electrodes 8 is selected such that the electrodes 23, 24 with opposite signs are not electrically connected to one another, i.e., are not short-circuited. This can be seen here from the indentations on the otherwise circular edge of the upper contacting electrode. On the rear side, a recess 25 can be seen, which causes a slight deviation from the circular base area and which serves to orient the piezo elements 2 with respect to a suitable counter component.

[0036] The Fig.4 shows a so-called tuning fork as an example of a design of the vibration sensor.

[0037] The mechanically oscillating unit 3 has two so-called fork tines connected to a diaphragm 5. On the opposite side of the diaphragm 5, in a housing 4 (shown here), there is a transducer device 1 with a plurality of disc-like piezo elements 2 arranged in a stack. The piezo elements 2 are clamped between a pressure screw 6 and a coupling element 7. The coupling element 7 for clamping relative to the diaphragm 5 has the shape of a hemisphere. List of reference symbols 1 converter device 2 piezo element 3 mechanically oscillating unit 4 housings 5 membranes 6 pressure screw 7 Coupling element 8 Contacting electrode 11 Insulating disc 12 locking lug 13th edition 20 Front side of the piezo element 21 Front side of the piezo element 22 Outer casing of the piezo element 23 Electrode 24 Electrode 25 recess QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 1 277 243 B1

[0004]

Claims

[1] Method for producing a converter device (1), wherein the transducer device (1) generates mechanical vibrations and / or receives mechanical vibrations, the method comprising at least the following steps: that at least two at least partially polarized piezo elements (2) are arranged relative to each other in such a way that one end face (20, 21) of the piezo elements (2) is in contact with each other and at least one electrode (23, 24) of the piezo elements (2) is located between the end faces (20, 21), that - preferably perpendicular to the end faces (20, 21) - a mechanical pressure is exerted on the at least two piezo elements (2), and that the at least two piezo elements (2) are connected to one another - in particular baked together - by the action of thermal energy over a predetermined period of time with a maximum temperature below a Curie temperature of the at least two piezo elements (2), while the mechanical pressure is exerted on them. [2] Method according to claim 1, wherein during the method a space between the contacting end faces (20, 21) is kept free of an adhesive. [3] Method according to claim 1 or 2, wherein the two piezo elements (2) are connected to each other by connecting electrodes (23, 24) located between the two piezo elements (2). [4] Method according to one of claims 1 to 3, wherein the two piezo elements (2) are arranged relative to each other in such a way that a contacting electrode (8) is located between the two piezo elements (2). [5] Method according to one of claims 1 to 4, wherein the piezo elements (2) are produced in such a way, that the piezo elements (2) each have two end faces (20, 21) and an outer casing (22), that an electrode (23, 24) is applied to each end face (20, 21), and that each electrode (23, 24) is guided from one end face (20, 21) of the two end faces (20, 21) via the outer jacket (22) to the respective other end face (21, 20) of the two end faces (20, 21). [6] Method according to one of claims 1 to 5, wherein a piezoelectric element (2) with at least one recess (25) in an outer casing (22) of the piezoelectric element (2) is used. [7] Method according to one of claims 1 to 6, wherein the piezo elements (2) are at least partially polarized before or after the application of the electrode (23, 24). [8] Method according to one of claims 1 to 7, wherein an odd number of piezo elements (2) are arranged relative to one another and connected to one another. [9] Method according to one of claims 1 to 8, wherein the maximum temperature is predetermined as a function of an application temperature range predetermined for the converter device (1). [10] A method according to any one of claims 1 to 9, wherein the method is part of a method for manufacturing a vibration sensor. [11] Vibration sensor, with a mechanically oscillatable unit (3) and with a converter device (1), wherein the transducer device (1) excites the mechanically oscillatable unit (3) to mechanical oscillations and / or receives mechanical oscillations from the mechanically oscillatable unit (3), and wherein the converter device (1) is manufactured using the method according to one of claims 1 to 10.

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