Vibration sensor

Abstract

The invention relates to a vibration sensor. A vibration element (10) arranged on a support element (11) has extensions of different sizes in two orthogonal directions (R1, R2). Two piezo-sub-components (20) are associated with the vibration element (10), wherein each piezo-sub-component (20) generates and / or receives mechanical vibrations in one of the two orthogonal directions (R1, R2). A piezo-component (20) is arranged in a recess (110) of the support element (11).

Description

[0001] Vibration sensor

[0002] The invention relates to a vibration sensor. The vibration sensor is preferably used to determine and / or monitor a process parameter of a medium. The process parameter is, for example, the fill level or the density, wherein the medium is, for example, a liquid, a gas, or a bulk material.

[0003] It is known in the art to use vibration sensors to detect whether liquids or bulk solids have reached or fallen below a limit level. Such sensors also allow, for example, the measurement of the medium's density. The measuring principle is based on the fact that a mechanically vibrating unit is excited to mechanical vibrations by a transducer device, and that the vibrations received by the transducer device are influenced by the interaction of the vibrating unit with the medium. The generated vibrations generally belong to the fundamental mode. The mechanically vibrating unit usually has one (in which case the sensor is a so-called single-rod) or two vibrating elements (this is a so-called tuning fork). The transducer device often has piezoelectric elements that serve to convert electrical signals into mechanical vibrations.

[0004] Ring- or disc-shaped piezoelectric elements are known, featuring polarization oriented from one end face to the other. Electrodes are located on these end faces, serving to apply and receive electrical signals. It is known to stack multiple piezoelectric elements to increase the force they can generate and / or to enhance their measurement sensitivity. Furthermore, piezoelectric elements are known that have at least two areas polarized in opposite directions. For example, bimorph piezoelectric elements are described in WO 2013 / 113446 A1. These consist of two essentially identical, homogeneously polarized piezoelectric elements whose end faces are connected. The polarization directions are opposite to each other. The two outer electrodes are used for generating and receiving vibrations.From DE 10 2012 100 728 A1, for example, it is known to insert disc-shaped piezoelectric elements directly into the so-called root region of vibration elements. The root region is the area where the support element transitions into the vibration elements mounted on it.

[0005] It has been shown that only two modes of the tuning fork are characterized by enabling a closed resonant circuit with minimal energy losses through the process connection and high mechanical quality. The first is a fundamental mode in which the two fork tines oscillate perpendicular to their paddle surfaces. They thus move periodically towards and away from each other. The second is a mode in which the fork tines move in a plane parallel to their paddle surfaces, and therefore in the direction of their greatest extent. They thus tilt alternately laterally away from each other and towards each other. These modes are described, for example, in DE 100 14 724 A1 or DE 10 2016 118445 A1.

[0006] The problem lies in the converter device, which must provide for the excitation or detection of the two modes.

[0007] The invention is based on the objective of proposing a vibration sensor whose transducer device allows the excitation and reception of the two different vibration modes.

[0008] The invention solves the problem by means of a vibration sensor, comprising at least one mechanically oscillating unit, a transducer device, and an electronic device, wherein the mechanically oscillating unit has at least one oscillating element and a support element, wherein the oscillating element is designed such that the oscillating element has different dimensions in two orthogonal directions by having a narrow side and a wide side, wherein the oscillating element is arranged on the support element, wherein the support element has at least one recess, wherein the transducer device excites the mechanically oscillating unit to mechanical vibrations starting from excitation signals of the electronic device and receives mechanical vibrations from the mechanically oscillating unit and transmits them as received signals to the electronic device.wherein the electronic device supplies the transducer device with the excitation signals in such a way that the oscillating element performs mechanical vibrations in the two orthogonal directions, wherein the transducer device has two piezoelectric components, wherein the two piezoelectric components are assigned to the oscillating element, wherein each of the two piezoelectric components generates and / or receives mechanical vibrations of the oscillating element in one of the two orthogonal directions, and wherein at least one piezoelectric component of the two piezoelectric components is at least partially arranged in the recess.

[0009] The vibration sensor according to the invention has at least one oscillating element with different dimensions in two directions. The oscillating element, for example, has a paddle shape. This different effective area results in different interactions with the surrounding medium during vibrations in the two directions. Therefore, the vibrations allow for different conclusions to be drawn about the medium and its properties. Two piezoelectric components are provided to excite the vibrations and to receive them for further processing and evaluation. Each piezoelectric component excites one vibration mode. This allows for a simple and robust design of the piezoelectric components, as they are only connected to vibrations in one direction. The only requirement is that the electronic device be appropriately designed to correctly generate, receive, and process the vibrations.Each piezoelectric component consists of at least one piezoelectric element. Alternatively, it can be a stack of at least one piezoelectric element. Depending on the design, the piezoelectric elements are disk-shaped or ring-shaped. Furthermore, the piezoelectric elements can be homogeneously polarized or exhibit multiple polarization directions. Additionally, within a stack of piezoelectric elements, these elements can have either the same or opposite polarization directions.

[0010] In general, the orientations and positioning of the piezoelectric components and the associated oscillating element must be aligned with each other in relation to the respective vibration modes to be generated or received.

[0011] In one embodiment, the piezoelectric components are located only in the recess or recesses of the carrier element.

[0012] Depending on the design, the recess has, for example, a rectangular, square, circular, cross-shaped, X-shaped, or T-shaped base. Other variations include a double T-shape or an H-shape. In each variation, a bar shaped like the chosen letter serves to hold a piezoelectric component. The bars can be arranged in a common plane or one above the other.

[0013] One embodiment involves the two piezoelectric components being arranged together, at least partially, within the recess. In this embodiment, the piezoelectric components of the vibrating element are located in a common recess.

[0014] One embodiment includes a support element with at least two recesses, where the two recesses are assigned to the oscillating element, and where one of the two piezoelectric components is arranged in each of the two recesses. In this embodiment, each piezoelectric component has its own recess in the support element.

[0015] One embodiment consists in the vibration sensor further comprising at least one fixing component, in which the two piezoelectric components are arranged within the fixing component, and in which the fixing component is at least partially positioned within the recess. In this embodiment, the two piezoelectric components are combined into a single component by a fixing component, which is positioned within the common recess. The fixing component consists, for example, entirely or partially of a plastic material.

[0016] One embodiment includes a mechanically vibrating unit with two vibrating elements, a transducer device with two pairs of at least two piezoelectric components each, and each vibrating element being assigned a pair of at least two piezoelectric components. In this embodiment, the mechanically vibrating unit, which, for example, has two paddles as vibrating elements, is a so-called tuning fork. The transducer device has four piezoelectric components, forming two pairs of piezoelectric components. Each pair is assigned to a vibrating element. Thus, the electronic device is designed to coordinate the two pairs so that the vibrating elements perform appropriately antiphase vibrations. This ensures that no vibrational energy is lost through coupling with the support element.

[0017] The invention is explained in more detail with reference to the following figures.

[0018] Fig. 1 shows a spatial representation of a schematically depicted vibration sensor,

[0019] Fig. 2 shows a section through the sensor of Fig. 1 ,

[0020] Fig. 3 shows a top view of the inside of a vibration sensor according to a first embodiment,

[0021] Fig. 4 shows an assembly of part of the transducer device of a vibration sensor according to a second embodiment,

[0022] Fig. 5 shows a top view of the inside of a vibration sensor according to a second embodiment,

[0023] Fig. 6 shows a top view of the inside of a vibration sensor according to a third embodiment,

[0024] Fig. 7 shows an enlarged view of a piezoelectric component as used in the third embodiment of Fig. 6, and Fig. 8 shows a section through the two piezoelectric components that are associated with a vibrating element of a fourth embodiment.

[0025] Fig. 1 shows the basic structure of a vibration sensor.

[0026] The housing 4, which here is designed as a circular cylinder, terminates at its end face with a very thick support element 11. Two vibration elements 10 are attached to the support element 11, acting as prongs of the mechanically vibrating unit 1. The vibration elements 10 have a paddle-like shape, with a wide side 102 facing direction R1 and a narrow side 101 facing direction R2. The two directions R1 and R2 are perpendicular to each other. Due to the paddle shape, the effective surface is different in each direction, so that the medium can also affect the vibrations differently in each direction.

[0027] The transducer device 2 – shown in Fig. 2 – excites the mechanically vibrating unit 1 to oscillations and receives these oscillations. The electronic unit 3 generates electrical excitation signals to excite the oscillations. The electronic unit 3 evaluates the electrical signals generated by the transducer device 2 in response to the oscillations with respect to process variables. These include, for example, the degree of coverage of the mechanically vibrating unit 1 by a medium, or the density and / or viscosity of the medium with which the mechanically vibrating unit 1 is in contact.

[0028] In this embodiment, the electronic unit 3 generates excitation signals such that the oscillating elements 10 perform antiphase oscillations in the two directions R1 and R2. In particular, they oscillate along direction R1, so that only the narrow sides 101 interact with the medium. In the other case, the oscillating elements 10 oscillate in direction R2, and the wider sides 102, with their significantly larger area, interact with the medium.

[0029] Fig. 2 shows that the transducer device 2 consists of two sub-units. These sub-units are arranged here in the support element 11 and each is aligned with a vibration element 10. The piezoelectric components 20 are each located in a recess 110 of the support element 11. Because of this positioning, the transducer device 2 can also be referred to as a root drive. The support element 11 forms the base of the cup-shaped housing 4.

[0030] By making the converter device 2 consist of two sub-units, the oscillating elements 10 can each be excited in opposite phases so that the forces acting on the support element 11 exactly compensate each other.

[0031] Fig. 3 shows the inner side of the support element 11 facing the interior of the housing 4. The two recesses 110 are visible, above which – on the outer side of the support element 11 – the vibration elements 10 are located. In this example, the vibration elements 10 and the recesses 110 are arranged relative to each other such that the long sides 102 of the vibration elements 10 are parallel to the long sides of the rectangular recesses 110. In other words, the recesses 110 are oriented appropriately below the projection of the vibration elements 10.

[0032] Each oscillating element 10 is assigned two piezoelectric components 20. The transducer device 2 thus has four piezoelectric components 20 in this configuration. The piezoelectric components 20 are arranged such that one component 20 is parallel to the wide side 102 and one component 20 is parallel to the narrow side 101 of the assigned oscillating element 10. This allows one component 20 to generate or receive vibrations in one direction R1 and the other component 20 to generate or receive vibrations in the perpendicular direction R2.

[0033] The piezoelectric components 20 are designed in a disc shape – alternatively, several disc-shaped piezoelectric components 20 are arranged in a stack – and have a polarization oriented from one end face to the other. This is indicated here by the plus and minus signs for polarization. When an alternating voltage is applied to the end faces, the piezoelectric components 20 contract or expand in the direction perpendicular to the sides 101, 102 of the oscillating elements 10. This then causes the mechanically oscillating unit to move across the support element 11.

[0034] It can be seen that the piezoelectric components 20, which are arranged parallel to the narrow side 101, are mirror images of each other. This serves to simplify the implementation of the antiphase nature of the oscillations.

[0035] Fig. 4 shows part of an extension of the design shown in Fig. 3.

[0036] In this case, two piezoelectric components 20 are arranged parallel to the same side – here the narrow side 101 – of the vibration elements 10. The three piezoelectric components 20 are arranged in a fixing component 5, which is inserted into the recess 110. This simplifies manufacturing and ensures the correct orientation of the components.

[0037] In an alternative variant - not shown - two piezoelectric component parts 20 of the long side 102 are assigned to the oscillating element 10.

[0038] Figure 5 shows a variant with four piezoelectric components 20 per vibrating element 10. Two piezoelectric components 20 are arranged parallel to each other and parallel to one side 101, 102 of the vibrating element 10.

[0039] In Fig. 6, the carrier element 11 has four recesses 110, each containing a piezoelectric component 20. Two recesses 110 are assigned as a pair to each vibrating element 10 and are oriented parallel to the wide side 102 and narrow side 101, respectively.

[0040] Figure 6 shows an example of the orientation of the individual recesses 110 and thus of the piezoelectric components 20 relative to each other. The orientations shown in the preceding embodiments can be implemented accordingly, such that each piezoelectric component 20 is assigned a recess 110. The recesses 110, located radially outward in the example shown, are arranged parallel to the wide sides 102 and each has a piezoelectric component 20 of the shape already discussed above. The polarization thus runs from one end face to the other, and when subjected to an electrical signal, the piezoelectric component either expands or contracts along the polarization.

[0041] The two other recesses 110 are oriented parallel to the narrow sides 101, and, unlike the previously discussed recesses 110, are located centrally to the wide side 102 and therefore not near an end of the paddles of the oscillating elements 10. The piezoelectric components 20 are each bimorph piezoelectric elements, consisting of two individual piezoelectric elements that are contacted with each other via their end faces and whose polarizations are directed either away from each other or towards each other.

[0042] Fig. 7 shows a piezoelectric component 20 located in this central recess 110. A bimorph piezoelectric element can thus be identified, in which the positive poles of the two piezoelectric elements are located in the middle and the negative poles on the outside.

[0043] Figure 8 shows how two piezoelectric components 20, which are associated with a vibration element, can be arranged. In this case, the recess 110 has the shape of a cross when viewed from above on the support element 11. Here, in the side view of the section, the capital letter T is visible with the piezoelectric components 20, which are located in different planes. Thus, there are two essentially flat, cube-like sub-components that intersect at right angles. The two piezoelectric components 20 are arranged above each other.

[0044] In Fig. 8, one can therefore see the narrow side of one – here upper – piezoelectric component 20 and below it the wide side of the other – here lower – piezoelectric component 20. The two piezoelectric components 20 preferably excite the two modes of the oscillating element, which is positioned appropriately on the support element 11 above the recess 110 and therefore above the two piezoelectric components 20.

[0045] Reference symbol

[0046] 1 mechanically oscillating unit

[0047] Converter device

[0048] electronic device

[0049] Housing

[0050] 5 Fixation component

[0051] 10 oscillating element

[0052] 11 Support element

[0053] 20 Piezoelectric components

[0054] 101 narrow side

[0055] 102 wide side

[0056] 110 recess

[0057] R1, R2 directions

Claims

Patent claims 1. Vibration sensor, comprising at least one mechanically oscillating unit (1), a transducer device (2), and an electronic device (3), wherein the mechanically oscillating unit (1) comprises at least one oscillating element (10) and a support element (11), wherein the oscillating element (10) is configured such that the oscillating element (10) has different dimensions in two orthogonal directions (R1, R2) by having a narrow side (101) and a wide side (102), wherein the oscillating element (10) is arranged on the support element (11), wherein the support element (11) has at least one recess (110).wherein the transducer device (2) excites the mechanically oscillating unit (1) to mechanical vibrations starting from excitation signals of the electronic device (3) and receives mechanical vibrations from the mechanically oscillating unit (1) and transmits them as received signals to the electronic device (3), wherein the electronic device (3) supplies the transducer device (2) with the excitation signals such that the oscillating element (10) performs mechanical vibrations in the two orthogonal directions (R1, R2), wherein the transducer device (2) has two piezoelectric components (20), wherein the two piezoelectric components (20) are assigned to the oscillating element (10), wherein each of the two piezoelectric components (20) generates and / or receives mechanical vibrations of the oscillating element (10) in one of the two orthogonal directions (R1, R2),and wherein at least one piezo component of the two piezo sub-components (20) is at least partially arranged in the recess (110).

2. Vibration sensor according to claim 1, wherein the two piezoelectric components (20) are jointly at least partially in are arranged in the recess (110).

3. Vibration sensor according to claim 1, wherein the carrier element (11) has at least two recesses (110), wherein the two recesses (110) are associated with the oscillating element (10), and wherein one of the two piezoelectric component parts (20) is arranged in each of the two recesses (110).

4. Vibration sensor according to claim 1 or 2, wherein the vibration sensor further comprises at least one fixing component (5) wherein the two piezoelectric component components (20) are arranged in the fixing component (5), and wherein the fixing component (5) is at least partially arranged in the recess (110).

5. Vibration sensor according to one of claims 1 to 4, wherein the mechanically oscillating unit (1) has two oscillating elements (10), wherein the transducer device (2) has two pairs of at least two each has piezoelectric component parts (20), and wherein each oscillating element (10) is assigned a pair of at least two piezoelectric component parts (20).

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