Vibration sensor having a propeller drive

Abstract

The invention relates to a vibration sensor. A transducer device (2) excites a mechanically vibrating unit (1) to perform vibrations and / or receives vibrations from this unit. The mechanically vibrating unit (1) has at least one vibrating element (10). The transducer device (2) has a piezoelectric component (3) having two vibration directions (40) and is assigned to the vibrating element (10). The vibration directions (40) enclose an offset angle with each other.

Description

[0001] Vibration sensor with propeller drive

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

[0003] It is known in the art to use vibration sensors to detect whether liquids or bulk solids have reached or fallen below a certain threshold level. Such sensors also allow, for example, the measurement of the density of the medium. The measuring principle is based on the fact that a mechanically oscillating unit is excited to mechanical vibrations by a transducer device, and that the received vibrations are influenced by the interaction of the oscillating unit with the medium. The generated vibrations generally belong to the fundamental mode.

[0004] It is known to excite the mechanically oscillating unit to oscillate in different directions in order to obtain different information about a medium to be measured or about the mechanically oscillating unit itself (see, for example, DE 100 14 724 A1, EP 0 903 563 A1, DE 10 2017 130 527 A1, DE 101 38 360 A1, WO 2011 / 018312 A1, or DE 10 2016 118 445 A1). If a flat (paddle-like) prong oscillates parallel to its prong surface, a covering liquid will only slightly reduce the oscillation frequency, so that the frequencies in air (i.e., uncovered) and in the medium are approximately the same. However, if the tine oscillates perpendicular to the tine surface, the liquid coating creates a large frequency difference, as a large amount of the medium's mass is moved by the effective area of ​​the oscillating element. The moving mass depends on the density and viscoelasticity of the medium.The same applies to the vibration amplitude, which for resonators with forced vibrations depends on the mechanical quality of the vibration sensor. Thus, a measurement can be performed by evaluating, for example, the frequency or amplitude ratio between two orthogonal vibrations, particularly between parallel and perpendicular vibrations. The change in frequency and amplitude depends on the type of medium. For example, parallel and perpendicular vibrations do not differ in frequency and amplitude in gaseous media. In liquids, the frequency of the parallel vibrations is higher than that of the perpendicular vibrations. The same applies to the amplitude. In highly viscous liquids or bulk materials, no vibration at all may be possible.

[0005] To excite or receive vibrations, a transducer device is typically present that converts between electrical signals and mechanical vibrations. Piezoelectric elements are often used for this purpose. These can be arranged in a stack, for example (see, for example, WO 01 / 66269 A1). Alternatively, so-called bimorph drives are used (see, for example, DE 10 2004 010 992 B3 or DE 100 14 724 A1). These are usually discs polarized in opposite directions. DE 44 33 679 A1 discloses a vibration exciter with differently polarized piezoelectric layers. JP 63-65708 shows a similar design.

[0006] The invention is based on the object of proposing a vibration sensor in which it is possible to generate or receive vibrations in different directions.

[0007] The invention solves the problem by means of a vibration sensor having at least one mechanically oscillatable unit and a transducer device, wherein the transducer device excites the mechanically oscillatable unit to mechanical oscillations and / or receives mechanical oscillations from the mechanically oscillatable unit, wherein the mechanically oscillatable unit has at least one oscillating element, wherein the transducer device has at least one piezo component, wherein the piezo component is assigned to the oscillating element, wherein the piezo component has at least two oscillation directions, and wherein the oscillation directions enclose an offset angle with one another.

[0008] The vibration sensor consists of a mechanically oscillating unit and a transducer device. The transducer device is used to excite the mechanically oscillating unit to oscillate and / or receive mechanical vibrations from the mechanically oscillating unit. The vibrations (particularly frequency and / or amplitude) depend on the process variable to be measured or monitored, so that the process variable can be inferred from the evaluation of the received vibrations.

[0009] The mechanically oscillatable unit has at least one oscillating element. The oscillating element is, for example, a membrane, a single rod, or a paddle. Alternatively, the mechanically oscillatable unit can also have two oscillating elements, so that overall it is a tuning fork with two so-called fork tines as oscillating elements. In one embodiment, more than two oscillating rods are present. Preferably, the number of oscillating rods is an integer multiple of two, with the oscillating rods arranged in pairs. The at least one oscillating element can be designed in any desired manner; only examples have been given. Combinations of the aforementioned examples are also possible for the oscillating element. The transducer device has at least one piezo component assigned to the oscillating element. The piezo component therefore receives the vibrations of this oscillating element or excites precisely this oscillating element to oscillate.The piezo component has at least two directions of vibration. One direction of vibration is defined by the direction or axis along which the piezo component at least partially expands and contracts. Thus, the direction of vibration is also the direction in which the vibrating element is excited to vibrate and from which vibrations are received and converted into electrical signals. The piezo component is preferably also at least partially polarized in this direction.

[0010] The two different vibration directions enclose an angle, referred to here as the offset angle. The piezo component thus allows vibrations in different directions, preferably offset by 90° from each other. Therefore, the vibrating element is also excited to vibrate in two different directions (preferably at an angle of essentially 90° to each other) or can receive vibrations from two different directions.

[0011] In one embodiment, the vibration directions are generated with an excitation signal offset from one another in time, so that the vibrating element is only excited to vibrate in one vibration direction at a time.

[0012] In an alternative embodiment, the two vibration directions are generated or received essentially simultaneously.

[0013] One embodiment involves the offset angle being substantially 90°. In this embodiment, the vibration directions of the piezo component are perpendicular to one another. Accordingly, in this embodiment, the associated vibration element executes vibrations in mutually perpendicular directions, or vibrations of the vibration element can be received from mutually perpendicular directions. In one embodiment, these vibrations are, in particular, parallel or perpendicular to a surface of the substantially flat or paddle-shaped vibration element.

[0014] One embodiment provides for the piezo component to be designed as a single piece. In this embodiment, the piezo component is produced, for example, by a 3D printing process, to form a unit having two different directions of vibration. In one embodiment, two different sections of the piezo component are assigned to the different directions of vibration. An alternative embodiment includes the piezo component having at least two piezo elements, each of the two piezo elements having a direction of vibration, and the two piezo elements being arranged such that the directions of vibration enclose the offset angle with one another. In this embodiment, the piezo component thus has at least one piezo pair with two piezo elements, each of which has its own direction of vibration.

[0015] The following describes the designs of the two individual piezo elements.

[0016] One embodiment provides that the two piezo elements are arranged one behind the other along a longitudinal axis of the associated oscillating element. In this embodiment, the two piezo elements are arranged along an axis at different heights. The axis is preferably a longitudinal axis of the oscillating element. The two piezo elements therefore oscillate in different directions and at different positions. Depending on the embodiment, the piezo elements can be arranged along the longitudinal axis in the region of the extension of the oscillating element or can be arranged upstream or downstream of the oscillating element. In this embodiment, it is also provided in particular that the oscillating element is designed such that a longitudinal axis is present. Therefore, it is preferably a single rod as the oscillatable unit or a fork tine as the oscillating element.If, for example, the oscillating element has a paddle shape, the longitudinal axis is preferably formed by the support to which the paddle is attached.

[0017] In an alternative design, the two piezo elements are located at the same height along the axis. For this purpose, the piezo elements are designed, for example, in the shape of the capital letters T, L, or X.

[0018] One embodiment involves the two piezo elements being mechanically coupled to each other via a coupling component. In this embodiment, there is a coupling component through which the two piezo elements are mechanically coupled to each other. This means that the piezo elements are also individually mechanically coupled to the coupling component. Thus, the piezo elements transmit vibrations to the coupling component and receive vibrations from the coupling component. In one embodiment, the piezo elements are glued to the coupling component.

[0019] The following configurations refer to implementations of the coupling component.

[0020] One embodiment provides that the coupling component comprises a sheet metal strip with two strip surfaces that are rotated relative to each other by the offset angle. The sheet metal strip can be made of any metal (e.g., stainless steel or brass) or at least partially of a metal or metal mixture. As a strip, the sheet metal strip has a significantly greater length than width, with the thickness also being small in relation to the length or width. Two surfaces of the strip are rotated relative to each other by the aforementioned offset angle. A piezo element is preferably arranged on each strip surface. This shape of the surfaces rotated relative to each other results in the coupling component in question appearing similar to a propeller. Since the coupling component, together with the piezo elements, can function as a drive, among other things, this embodiment can also be described as a vibration sensor with a propeller drive.

[0021] One embodiment consists in the coupling component being arranged at least partially within the oscillating element. In this embodiment, the oscillating element has a recess or is at least partially hollow. The coupling component, which thus receives the vibrations of the piezo elements as the first component from the piezo component or transmits them to the piezo component as the last component, is located in the associated oscillating element and is also mechanically coupled to it. The coupling component is preferably glued and / or encapsulated.

[0022] In an alternative embodiment, the mechanically oscillatable unit further comprises a base body, and the coupling component is arranged at least partially in or on the base body. The oscillating element is mechanically coupled to the base body. The base body can be designed as a membrane or as a sufficiently solid (metal) block. The base body is preferably designed to serve as a housing for the electronics or the transducer device. The mechanically oscillatable unit is preferably attached to an end face of the base body.

[0023] One embodiment provides that the associated oscillating element forms the coupling component. In this embodiment, the piezo elements are directly connected to the oscillating element.

[0024] One embodiment consists in that the oscillating element has a paddle component and a support component, and that a piezo element is arranged on each of the paddle component and on the support component. In this embodiment, the oscillating element has a paddle shape. A paddle is essentially characterized in that it has a wide surface and a narrow surface or side, preferably arranged perpendicular to this. The paddle is preferably attached to a type of support component, which can alternatively also be referred to as a column or post. Depending on the embodiment, the support component can be in the form of a circular cylinder or in the form of a cuboid. The piezo elements are applied to the support component and to the paddle component, respectively. In one embodiment, a piezo element is located on the wide side of the paddle component.One embodiment provides that the mechanically oscillatable unit has two oscillating elements, that the transducer device has two piezo components, and that each oscillating element is assigned a piezo component. In an alternative embodiment, several oscillating elements are provided, which are preferably arranged in pairs.

[0025] In an alternative embodiment, there is only exactly one oscillating element, to which exactly one piezo component is assigned.

[0026] One embodiment consists in that the mechanically oscillatable unit further comprises a base body, that the mechanically oscillatable unit comprises at least one oscillating element, that the at least one oscillating element is mechanically coupled to an end face of the base body, that the piezo component is mechanically coupled to the end face, and that the end face has a circular cross-sectional area. The base body is preferably designed as a hollow cylinder with a circular base area. Therefore, one end face is also provided with a circular cross-sectional shape. In one embodiment, the oscillating element is designed separately and attached to the end face. Alternatively, the oscillating element is a component of the end face. The at least one oscillating element and the piezo component are mechanically coupled to the end face, such that in particular the mechanical vibrations can be transmitted via the end face.

[0027] In an alternative embodiment, it is provided that the mechanically oscillatable unit further comprises a base body, that the mechanically oscillatable unit has at least one oscillating element, that the at least one oscillating element is mechanically coupled to an end face of the base body, that the piezo component is mechanically coupled to the end face, and that the end face has a cross-sectional area that deviates from a circular shape - preferably elliptical, square, or rectangular. In this embodiment, the end face has an asymmetrical cross-section. The directions of oscillation of the piezo component and the end face are preferably arranged relative to one another such that the directions of oscillation correspond to the different dimensions of the end face. This results in different stiffnesses in the directions of oscillation and thus different resonance frequencies.For example, in the case that the two oscillations are excited simultaneously, the different resonance frequencies facilitate the subsequent signal evaluation.

[0028] The invention is explained in more detail with reference to the following figures. Fig. 1 shows a section through a first embodiment of a schematically illustrated vibration sensor,

[0029] Fig. 2 shows a spatial representation of a piezo component consisting of two piezo elements on a coupling component,

[0030] Fig- 3 shows three different designs (a), b), c)) of an alternative design of the coupling component,

[0031] Fig. 4 shows a schematic representation of a second embodiment of a vibration sensor and

[0032] Fig. 5 shows a section through a third embodiment of a vibration sensor.

[0033] Figure 1 shows a design of the vibration sensor in the form of a tuning fork. An enlarged detail is shown in Figure 2.

[0034] Of the two oscillating elements 10 of the mechanical oscillating unit 1, only one is shown in Fig. 1. As can be clearly seen, the oscillating element 10 has a paddle shape and is attached to a base body 6. The oscillating element 10 is located on an end face 60 of the hollow cylindrical base body 6, which, in addition to the converter device 2 and the wiring for contacting, preferably also houses further electronic components (not shown here). The oscillating element 10 and the end face 60, or rather the base body 6, are even constructed as a single piece.

[0035] The oscillating element 10 has a recess in which the transducer device 2 is located, which, based on an electrical excitation signal, both excites the mechanically oscillating unit 1 to oscillate and receives its oscillations and converts them into an electrical reception signal. An adhesive (not shown here) or a potting compound, e.g., epoxy resin, is preferably present in the recess. An evaluation unit (not shown here) can determine at least one process variable of a medium (not shown here) based on the reception signals. This is, for example, the fill level of a liquid or bulk material in a container.

[0036] Of the transducer device 2, only one piezo element 4 is shown, which (see Fig. 2) is located on a coupling component 5. Fig. 1 indicates that electrical contact between the two piezo elements 4 is established via two lines. Furthermore, it is indicated that the different vibration directions 40 are related to the piezo elements 4. In particular, the piezo element 4—here, the lower one—is oriented like the illustrated paddle-shaped side of the vibration element 10.

[0037] Fig. 2 shows the coupling component 5 of Fig. 1, which is designed as a sheet metal strip.

[0038] The top surface of the sheet metal strip is divided into two separate strip surfaces 50, which are rotated relative to each other. Since the offset angle here is 90°, the strip surfaces 50 are also rotated at right angles to each other.

[0039] On each of the two strip surfaces 50 there is a flat piezo element 4 of the - here multi-part - piezo component 3. The two piezo elements 4 are each polarized in one direction, wherein the polarization direction is perpendicular to the base surface of the piezo element 4 and thus also perpendicular to the respective strip surface 50.

[0040] If an electrical voltage is applied to a piezo element 4, mechanical vibrations occur in the respective vibration direction 40. This is indicated here by the two arrows. The piezo component 3 can thus generate mechanical vibrations in two mutually perpendicular directions or receive mechanical vibrations from two directions. These two directions are perpendicular to each other in the illustrated embodiment.

[0041] Fig. 3 shows three different designs of a coupling component 5 (a, b and c).

[0042] In the variant shown in Fig. 3 a), the coupling component 5 has a substantially cross-shaped configuration. The two axes result in a total of eight flanks on which the piezo elements 4 can be mounted.

[0043] The variant shown in Fig. 3 b) has a T-shape, and the coupling component 5 shown in Fig. 3 c) has an L-shape. In both variants, the piezo elements 4 can alternatively be mounted on the sides not shown.

[0044] It is relevant that the offset angle (here 90°) between the vibration directions to be achieved or received is maintained during the design and placement of the piezo elements 4.

[0045] For the L-shape shown in Fig. 3 c), a rectangular recess is provided in an oscillating element in one application example. The two legs of the L-shaped coupling component 5 rest against the inner walls of the recess. In general, there is a wide range of materials available for the coupling component 5. For example, the coupling component 5 can be made of a relatively rigid material. However, it is also possible for the coupling component 5 to be flexible to a certain extent.

[0046] The embodiment of Fig. 4 indicates how the vibration directions 40 of the piezo elements 4 are connected to the geometry of the vibration elements 10 (cf. Fig. 2).

[0047] The vibration sensor is—as in the embodiment of Fig. 1—a tuning fork with two paddle-shaped vibrating elements 10 connected to a base body 6, of which only the end face 60 is shown here. The difference from the embodiment of Fig. 1 is that the vibrating elements 10 themselves serve as coupling components 5 between the individual piezo elements 4 of the respective piezo component 3 or between the piezo component 3 and the respective vibrating element 10. The piezo components 3 are directly coupled to the respective associated vibrating element 10.

[0048] The oscillating elements 10 have a column- or rod-shaped support component 102, which is connected to the base body 6 on one side, and a paddle component 101, each of which is connected to the support component 102. A piezo element 4 is attached to each of the support component 102 and the paddle component 101. It is indicated that the piezo elements 4 are rotated relative to one another at an offset angle, which is 90° here. Thus, one piezo element 4 is located with its wide surface on the flat side of the oscillating element 40, and the other piezo element 4 is located perpendicular to it, so that only the narrow side can be seen. It is also shown that the piezo elements 4 are arranged at different heights along the longitudinal axis 100 of the respectively assigned oscillating element 10. In an alternative embodiment - not shown here - the piezo elements 4 are at the same height.

[0049] Fig. 5 shows a design with a single rod as the only oscillating element 10.

[0050] The piezo elements 4 of the piezo component 3 are mounted in the interior of the hollow oscillating element 10, so that the coupling component 5 is identical to the oscillating element 10. The piezo elements 4 are fixed in such a way that they are offset from one another along their longitudinal axis and emit and receive their oscillation energy in different directions. The oscillation direction is perpendicular to the large-surface side of the piezo element 4.

[0051] In the illustrated embodiment, the oscillating element 10 is supplemented by a separate paddle on the front side. Reference symbols: mechanically oscillating unit

[0052] converter device

[0053] Piezo component

[0054] Piezo element

[0055] coupling component

[0056] Basic body

[0057] Oscillating element

[0058] Direction of oscillation

[0059] Band area

[0060] Front side of the base body

[0061] Longitudinal axis

[0062] Paddle component

[0063] Carrier component

Claims

Patent claims 1 . Vibration sensor, with at least one mechanically oscillatable unit (1) and a Transducer device (2), wherein the transducer device (2) excites the mechanically oscillatable unit (1) to mechanical oscillations and / or receives mechanical oscillations from the mechanically oscillatable unit (1), wherein the mechanically oscillatable unit (1) has at least one oscillating element (10), wherein the transducer device (2) has at least one piezo component (3), wherein the piezo component (3) is assigned to the oscillating element (10), wherein the piezo component (3) has at least two oscillation directions (40), and wherein the oscillation directions (40) enclose an offset angle with one another.

2. Vibration sensor according to claim 1, wherein the offset angle is substantially 90°.

3. Vibration sensor according to claim 1 or 2, wherein the piezo component (3) has at least two piezo elements (4), wherein each of the two piezo elements (4) has a direction of vibration (40), wherein the two piezo elements (4) are arranged such that the directions of vibration (40) enclose the offset angle with each other, and wherein the two piezo elements (4) are mechanically coupled to each other via a coupling component (5).

4. Vibration sensor according to claim 3, wherein the two piezo elements (4) are arranged one behind the other along a longitudinal axis (100) of the associated oscillating element (10).

5. Vibration sensor according to claim 3 or 4, wherein the coupling component (5) comprises a sheet metal strip with two strip surfaces (50) which are rotated relative to one another by the offset angle.

6. Vibration sensor according to one of claims 3 to 5, wherein the coupling component (5) is arranged at least partially within the oscillating element (10).

7. Vibration sensor according to one of claims 3 to 5, wherein the mechanically oscillatable unit (1) further comprises a base body (6), and wherein the coupling component (5) is arranged at least partially in or on the base body (6).

8. Vibration sensor according to claim 3 or 4, wherein the associated oscillating element (10) forms the coupling component (5).

9. Vibration sensor according to claim 8, wherein the oscillating element (10) has a paddle component (101) and a support component (102), and wherein a piezo element (4) is arranged on the paddle component (101) and on the support component (102).

10. Vibration sensor according to one of claims 1 to 9, wherein the mechanically oscillatable unit (1) has two oscillating elements (10), wherein the transducer device (2) has two piezo components (3), and wherein each oscillating element (10) is assigned a piezo component (3).

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