Vibration sensor
By using a bonded joint and closed element design in the vibration sensor, the problems of difficult alignment and unstable performance in the prior art are solved, more efficient electrical connection and signal transmission are achieved, and manufacturing complexity and errors are reduced.
Patent Information
- Application Number
- CN202480019155.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-03-27
- Filing Date
- 2024-03-27
- Publication Date
- 2025-10-24
AI Technical Summary
Existing vibration sensors are difficult to align during the bonding process, resulting in unstable performance, and electrical connectors are easily affected by stray modes and capillary effects, leading to signal errors and connection unevenness.
An adhesive joint is used to effectively connect the piezoelectric actuator to the diaphragm, and by setting a closing element and an electrical connector in the groove of the piezoelectric element, the capillary effect is reduced, the stability and symmetry of the electrical connection are ensured, and the influence of stray modes is reduced.
The invention improves the performance and signal accuracy of the piezoelectric actuator, simplifies the manufacturing process, reduces the difficulty of alignment, and enhances the stability of the bonded joint and the reliability of the electrical connection.
Smart Images
Figure CN120835984A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The invention relates to a vibration sensor according to claim 1. BACKGROUND
[0002] According to the prior art, known vibration sensors are used, for example, as vibration limit switches, wherein the vibration sensor has a diaphragm which can be excited to oscillate by means of a drive unit, whereby a mechanical oscillator, for example a vibration fork, which is arranged on the diaphragm, is usually excited to oscillate. Depending on the degree of coverage of the filling material on the mechanical oscillator and the viscosity of the filling material, the oscillator can oscillate with a characteristic frequency which can be detected by the vibration sensor and converted into a measurement signal. Such vibration sensors can also be referred to as electronic vibration sensors. Piezoelectric actuators having a piezoelectric element, for example a piezoelectric ceramic, and electrodes are usually used as electromechanical transducers in the drive unit of such sensors. A concept which is well known in this context is the use of an adhesive connection for fixing the piezoelectric actuator. The application of this concept is increasingly widespread because it can improve the performance, reduce the manufacturing costs and increase the automation capability compared to the case of a piezoelectric actuator with, for example, a threaded connection.
[0003] To this end, an adhesive layer can be applied to the diaphragm, a compensation element, for example a compensation ceramic, can be bonded to the diaphragm and an adhesive layer can be applied to the compensation ceramic, thereby creating an adhesive connection with the piezoelectric actuator. The piezoelectric actuator, in particular the electrode surface of its electrodes, can then be contacted by means of, for example, a flexible printed circuit board to create an electrical connection between the electrode surface and the electronics. The flexible printed circuit board can be a so-called flexible conductor.
[0004] The disadvantage in this case can be that the position and the rotational direction of the piezoelectric actuator have to be aligned very precisely before the adhesive is applied and that the piezoelectric actuator usually has to be fixed until the adhesive has cured. Furthermore, this alignment is usually difficult. Another disadvantage can be that the performance of the piezoelectric actuator is not as high as expected. Another disadvantage can be that the adhesive connection for operatively connecting the piezoelectric actuator to the diaphragm and which is implemented more thinly in order to achieve a good transfer of vibrations does not have sufficient stability or uniformity. Furthermore, this adhesive connection and the electrical connection between the electronics and the electrode surface can negatively influence each other. For example, this adhesive connection makes the creation of the electrical connection more difficult. SUMMARY
[0005] It is therefore an object of the present invention to provide a further improved vibration sensor.
[0006] This object is achieved according to the invention by the features of claim 1. Further practical embodiments and advantages will be explained in connection with the dependent claims.
[0007] The vibration sensor according to the present invention is used for detecting a fill level, a limit level, or for monitoring a process parameter and includes a diaphragm that can be set to vibrate. Furthermore, the vibration sensor according to the present invention includes a drive unit, wherein the drive unit includes a piezoelectric actuator. The piezoelectric actuator has a piezoelectric element and an electrode connected to the piezoelectric element. The electrode has an electrode surface. Furthermore, the vibration sensor according to the present invention includes a bonded joint, by which the piezoelectric actuator is effectively connected to the diaphragm, such that vibrations of the piezoelectric actuator can be transmitted to the diaphragm, and preferably, vibrations of the diaphragm can also be transmitted to the piezoelectric actuator. This bonded joint can also be referred to as an assembly bonded joint. The piezoelectric actuator can be assembled in the sensor via the assembly bonded joint. Preferably, the piezoelectric actuator is used both to set the diaphragm to vibrate and to detect vibrations of the diaphragm. Therefore, the drive unit is, in particular, a bonded piezoelectric drive or a bonded piezoelectric actuator. Furthermore, the vibration sensor according to the present invention includes an electronic system and an electrical connector between the electronic system and the electrode surface. The piezoelectric element has a recess, and the electrical connector extends through the recess. An electrical conductor electrically connected to the electrode surface is arranged in the groove. The electrical conductor can be part of the piezoelectric actuator and can be a metallized layer of the wall of the groove of the piezoelectric element. The vibration sensor has a closing element for closing the groove.
[0008] In this way, a prerequisite is created for the case that the electrical connections have only a very small influence on the active surface of the piezoelectric element and influence it in a way that does not cause or only causes small stray modes. Effects can be reduced or avoided in which, due to the geometry of the piezoelectric actuator and the matching structure of the vibration fork, an asymmetry or misalignment of the piezoelectric actuator can be enhanced or amplified by stray modes in the case of external excitation. In this way, the performance of the piezoelectric actuator can be improved and its susceptibility to stray modes can be reduced. Thus, the piezoelectric drive can be particularly easily constructed to be symmetrical, for example rotationally symmetrical. Within the framework of this document, rotationally symmetrical means that a rotation by any desired angle around the axis of rotation coincides with itself. The vibration sensor according to the application is less sensitive to the position tolerance of the piezoelectric actuator. In the case of the vibration sensor according to the application, due to the enclosing element, a capillary effect of the recess, which can weaken the adhesive joint, can also be prevented or reduced. The reliability of the assembly adhesive can also be improved, since the assembly adhesive can be prevented or reduced from being drawn into or penetrating into the recess before it has cured. The strength of the assembly adhesive also depends on whether suitable adhesive menisci, i.e. adhesive beads or adhesive fillets, are formed at the edges. The reason for this is that these adhesive menisci can balance the mechanical stress distribution or avoid attack points for crack formation. In particular, the enclosing element can highly reliably prevent any unevenness or weakening of the assembly adhesive or prevent or reduce interference with the formation of adhesive menisci by the assembly adhesive. The extent to which the assembly adhesive penetrates into the recess can be reduced to the extent that adhesive menisci are formed, which, due to their shape and size, are particularly effective in preventing attack points for crack formation. By preventing or reducing the assembly adhesive from being drawn into or penetrating into the recess, a further advantage can also be achieved: the surfaces of the wall of the recess or its metallization are almost not covered by the assembly adhesive and thus no longer enable electrical contact. This can avoid or reduce the difficulties of the assembly adhesive when creating the electrical connections between the electronic system and the electrode surface.
[0009] This is particularly advantageous for small recesses, since the capillary effect of small recesses can be particularly strong. Thus, it is possible to use small recesses without impairing the quality of the adhesive joint. When using small recesses, the loss of the active surface of the piezoelectric element can be reduced. This can maximize the vibration amplitude of the piezoelectric actuator. Within the framework of this document, small recesses are in particular recesses with a diameter of less than 5 mm, 2 mm or 1 mm. Preferably, the recess has a diameter of more than 0.1 mm.
[0010] Preferably, the recess has a diameter of 0.8 mm. Recesses smaller than 0.8 mm have to be laser machined on the green body and cannot be machined by drilling anymore, so the manufacturing is simplified in the usual case of sufficiently small recesses.
[0011] The closing element preferably closes the recess in an air-tight manner. Thereby, air remaining in the recess, in particular air enclosed between the closing element and the adhesive of the assembly adhesive joint, can effectively counteract the capillary effect and effectively prevent or reduce the penetration of the adhesive of the assembly adhesive joint into the recess before curing due to the capillary effect.
[0012] The closing element can at least almost completely fill the recess. This means in particular that the closing element at least almost completely replaces the air in the recess. Thereby, the penetration of the adhesive of the assembly adhesive joint into the recess before curing thereof can be particularly effectively reduced or prevented.
[0013] Preferably, the closing element extends at least also on the side of the piezoelectric element facing away from the membrane.
[0014] The assembly adhesive joint has an area in contact with the electrode surface. Within the framework of this document, this area is particularly referred to as connection area. The connection area can constitute the entire assembly adhesive joint or almost the entire assembly adhesive joint. The adhesive meniscus of the assembly adhesive joint can adjoin the connection area on the outside and / or on the inside. What can be achieved by the closing element is that the adhesive meniscus has an at least almost constant thickness in the connection area. Thereby, prerequisites are created for an elastic, stable adhesive joint. The thickness can be between 20 pm and 80 pm. Furthermore, the closing element can enable the adhesive meniscus to be formed in an at least substantially undisturbed manner.
[0015] Preferably, the connection area of the adhesive joint is arranged in an annular manner around the recess. Preferably, the thickness of the adhesive joint within the connection area varies in the radial direction by less than 10% or 1% of the maximum thickness of the adhesive joint within the connection area.
[0016] If the diameter of the recess is less than 5 mm or 2 mm or 1 mm, the performance of the piezoelectric actuator can be particularly high, since only a small amount of the working surface of the piezoelectric element is lost due to the recess.
[0017] Preferably, the closing element is different from the compensation element and the membrane. In one embodiment, the closing element is at least also arranged in the recess. In one embodiment, the compensation element is at least also or only arranged on the side of the piezoelectric element facing away from the membrane.
[0018] The closing element is preferably designed as a contact element and is in electrical contact with the electrical conductor. Thereby, components can be saved and the manufacturing can be simplified.
[0019] The electrical conductor and / or the contact element are in particular part of an electrical connection between an electronic system and an electrode surface.
[0020] The electrical conductor can terminate in the recess or pass through the recess, i.e. also extend outside the recess. Preferably, the electrical conductor extends at least from a first side of the piezoelectric element facing the membrane to a second side of the piezoelectric element facing away from the membrane. The electrical conductor can comprise or be formed by a connection of the electrode. The electrical conductor preferably comprises or is formed by a metallization of a wall portion of the recess of the piezoelectric element.
[0021] The surface of the contact element that is able to electrically contact the metallization of the wall portion of the recess of the piezoelectric element can be greater than 10% or 25% of the surface of the wall portion of the recess of the piezoelectric element.
[0022] In one embodiment, the contact element comprises or is formed by an electrically conductive adhesive. The contact element can comprise an electrically conductive adhesive and further elements, in particular a contact pin.
[0023] If the contact element is bonded to the piezoelectric actuator or to the electrical conductor, in particular by means of an electrically conductive adhesive, an electrical contact to the electrical conductor can be produced particularly reliably and durably, and the recess can be closed particularly reliably and tightly.
[0024] If the contact element is bonded into the recess, a prerequisite can be created for a particularly large contact surface to the electrical conductor. Furthermore, the working surface of the piezoelectric element can not be affected or only slightly affected by the contact surface.
[0025] The contact element can be used to produce an electrical contact to an electrode or to an electrical conductor, in particular for connecting an electrical wire or a printed circuit board to the electrode. The contact element can comprise, for example, a solder tab or a plug contact. The plug contact can be crimpable.
[0026] If the contact element preferably comprises or consists of a contact pin, various advantages can be achieved. Furthermore, this again creates a prerequisite for a larger and / or working surface of the piezoelectric element that is not (or only slightly) impaired.
[0027] The adhesive and / or the electrically conductive adhesive of the assembly adhesive joint can comprise a filler.
[0028] The contact pin can have an outer dimension that is complementary to an inner dimension of the recess. For example, the outer diameter of the contact pin can be slightly smaller than the inner diameter of the recess. Preferably, the outer diameter of the contact pin and the inner diameter of the recess are mutually adapted so as to maintain a minimum gap so that a filler of the electrically conductive adhesive can still enter the gap. Preferably, the contact pin has a curved surface arranged in the recess, more preferably the curved surface is in electrical contact with the piezoelectric actuator.
[0029] Preferably, the contact pin has a collar which can be bonded to the piezoelectric actuator. Thereby, the mechanical connection and / or the electrical contact of the contact pin to the piezoelectric actuator can be improved.
[0030] If the contact pin is part of an electrical plug connection, components such as separate plug contacts can be dispensed with.
[0031] In one embodiment, the vibration sensor comprises a printed circuit board with electronic components. Preferably, the contact element electrically and / or mechanically connects the piezoelectric actuator, in particular the electrical conductor, with the printed circuit board. The mechanical connection can be stable, i.e. any relative movement between the piezoelectric actuator or the electrical conductor and the printed circuit board is prevented.
[0032] In particular when the contact element is formed by an electrically conductive adhesive, the piezoelectric actuator can be directly mechanically and / or electrically connected with the printed circuit board. Thereby, components such as contact pins can be dispensed with.
[0033] In exemplary embodiments in which the contact pin is in particular not part of an electrical plug connection, the electrical plug contacts can be arranged on the printed circuit board.
[0034] The contact element can have two sides and be in contact with the piezoelectric actuator or the electrical conductor directly or via an electrically conductive adhesive with one side and with the printed circuit board directly or via an electrically conductive adhesive with the other side.
[0035] The electronic system of the vibration sensor can comprise or be formed by the electronic components of the printed circuit board.
[0036] Preferably, an additional electrode is arranged on the side of the piezoelectric element which faces away from the diaphragm. Preferably, the vibration sensor comprises an additional contact element for making electrical contact with the additional electrode.
[0037] If the additional contact element comprises an additional contact pin which is preferably bonded to the additional electrode, a prerequisite for a particularly reliable overall contact of the piezoelectric actuator is created. The additional contact pin can have a thickening at the end in order to increase the contact area and / or the bonding area with the additional electrode. The thickening can be disc-shaped.
[0038] If the contact pin and preferably the additional contact pin are part of an electrical plug connection, the vibration sensor particularly comprises a plug connection bonded on the piezoelectric actuator. The plug connection can replace the flexible conductor. Preferably, the electrical plug connection is standardized. In particular, the distance of the contact pin from the additional contact pin is equal to the distance of a standardized plug system, which is referred to as raster size. Preferably, the contact pin and the additional contact pin serve as contacts for a mating plug. To this end, the contact pin can have a recess in the form of a blind hole, respectively, which can provide a sleeve portion of the respective contact pin for receiving a mating plug contact. Alternatively, the contact pin can be configured to be contacted from the outside by a mating plug contact, for example by a spring contact.
[0039] Within the framework of the present document, the vibration sensor is also referred to simply as sensor. Within the framework of the present document, the term "piezoelectric element" refers to the portion formed of piezoelectric material in the piezoelectric actuator, for example a piezoelectric wafer. The piezoelectric element can be, for example, a piezoelectric crystal or a piezoelectric ceramic.
[0040] Preferably, the piezoelectric element has a first side facing the diaphragm. Within the framework of the present document, the term "electrode surface" particularly refers to a portion of the electrode which is arranged, preferably exclusively, on the first side of the piezoelectric element. The electrode surface is preferably annular. Preferably, the piezoelectric element has a second side facing away from the diaphragm. Preferably, the recess extends through the piezoelectric element, in particular from the first side to the second side. The recess can be in the form of a bore, and the wall portion of the recess can be a hollow cylinder.
[0041] The electrode surface is arranged in the sensor, preferably between the piezoelectric element and other components, for example a compensation element or the diaphragm, i.e. not easily accessible. Preferably, the electrode surface is covered, in particular completely covered, by a bonding joint.
[0042] The electrical connection can contact the electrode, in particular the electrode surface. Preferably, the electrode surface can be contacted from the side of the piezoelectric element facing away from the diaphragm, i.e. usually from above, through the recess. Such a contact is produced in particular around the piezoelectric element or around the edge of the piezoelectric element formed by the recess, and can therefore also be referred to as overmoulding.
[0043] One region of the piezoelectric actuator is preferably used to set the diaphragm into vibration. Preferably, the piezoelectric actuator does not have separate regions for exciting and detecting the diaphragm vibration. In a preferred design variant, a common region of the piezoelectric actuator is used both to set the excitation into vibration and to determine the frequency and / or amplitude of the diaphragm vibration. The common region of the piezoelectric actuator can be used, for example, alternately as transmitter and receiver. Preferably, the electrode is electrically isolated from the diaphragm.
[0044] In particular, the electronic system is an electronic component or assembly for providing driving energy to the piezoelectric actuator and / or for evaluating signals detected by the piezoelectric actuator. The electronic system can be an evaluation electronic system. The electronic system is in particular connected to a power supply for the supply of power. The electronic system can be arranged within a housing for the isolation and shielding of the electronic system.
[0045] Within the framework of the present document, the term "electrical connection between the electronic system and the electrode surface" in particular refers to the sum of all elements that electrically connect the electrode surface with the electronics. Preferably, the electrical connection extends partly inside the recess and partly outside the recess. The electrical connection preferably comprises a contact with the piezoelectric actuator, in particular a contact with the piezoelectric actuator by means of a contact element. The electrical connection can comprise an electrical line, for example a cable and / or a flexible printed circuit board. The electrical connection can comprise a contact of the electrical line or printed circuit board with the electrode, connection or contact element. The contact can comprise a conductive adhesive. The contact can be realized by soldering and / or clamping. The contact of the piezoelectric actuator in particular comprises a contact of an electrical conductor arranged in the recess, thus in particular a contact of a metallization layer of a wall portion of the recess.
[0046] The electrical connection can be a soldered connection, an adhesive connection and / or a fused connection, in particular between the electrical line and / or printed circuit board and the electrode or electrode surface or contact element. The adhesive joint is preferably realized by means of a conductive adhesive. The printed circuit board can be made of a rigid or flexible material. The printed circuit board can also be referred to as a circuit board.
[0047] Preferably, the piezoelectric element extends in one plane. Preferably, the piezoelectric element in particular has a bottom surface that lies in this plane. If the electrical connection that lies in the plane of the piezoelectric element does not protrude beyond the contour of the piezoelectric element, the sensor can have a particularly compact construction. If the piezoelectric element has a shape of a circular ring disc (one circular ring each on the top side and the bottom side), the bottom surface refers to the surface of one of the circular rings.
[0048] If the assembly adhesive is conductive and preferably forms the electrode surface, a particularly simple structure can be obtained.
[0049] Preferably, the assembly adhesive is not conductive. In this way, it can have a particularly thin thickness and be able to transmit vibrations with particularly low losses. Furthermore, the strength of the adhesive of the assembly adhesive can be particularly high.
[0050] If the recess extends through the center of the piezoelectric element, a further prerequisite is created for the electrical connection or the recess not to impair the working surface of the piezoelectric element, thus avoiding the generation of stray patterns. Furthermore, this also creates a prerequisite for avoiding the need for alignment of the rotational position of the piezoelectric actuator before the adhesive is applied.
[0051] The piezoelectric element or piezoelectric actuator can be disc-shaped. Preferably, the piezoelectric element or piezoelectric actuator is ring disc-shaped, preferably with a circular contour. The piezoelectric element or piezoelectric actuator can be rotationally symmetrical. The recess can extend in the region of the axis of rotation of the piezoelectric element or piezoelectric actuator or in a manner parallel to the axis of rotation of the piezoelectric actuator or piezoelectric element.
[0052] Preferably, the electrode is not a separate component, but a metallized surface of the piezoelectric element. The electrode is preferably formed as a metallized layer which is applied planarly on the piezoelectric element. Preferably, the electrode surface is planar, i.e. extends in only one plane.
[0053] The wall of the recess of the piezoelectric element is preferably inclined with respect to the first side of the piezoelectric element, in particular at approximately 90 degrees.
[0054] If the piezoelectric element is rotationally symmetrical about the axis of rotation and the electrode is point-symmetrical about the axis of rotation or rotationally symmetrical about the same axis of rotation, it is created as a prerequisite that neither the rotation of the piezoelectric actuator during assembly has any negative effects. Thus, it is possible to dispense with alignment means, such as alignment notches on the piezoelectric actuator, so that the working surface of the piezoelectric actuator can be increased. If the piezoelectric actuator is formed as a ring disc which is bonded in the sensor, in particular with a central wrap-around contact, the piezoelectric actuator is particularly insensitive to tolerances during assembly.
[0055] In addition to the electrode surface, the electrode can also have a connection. The connection can form an electrical conductor. The connection is preferably inclined with respect to the electrode surface. It can have a hollow-cylinder shape which transitions into the electrode surface in the edge region of the recess. Thus, the electrode can comprise a circular surface with a hole and a hollow cylinder adjoining the edge of the hole. Preferably, the hole coincides with the recess, and more preferably, the hole is arranged about the axis of rotation of the piezoelectric element or piezoelectric drive. The connection can extend into the recess of the piezoelectric element. The connection can comprise or be formed by a metallization of the wall of the recess of the piezoelectric element. Preferably, the metallization of the electrode or the electrode-forming metallization of the piezoelectric element extends seamlessly from the side of the piezoelectric element facing the diaphragm to the wall of the recess. If the electrical connection comprises the connection of the electrode, the electrode surface can be contacted particularly well.
[0056] If the connecting portion of the electrode has a region extending on the side of the piezoelectric element facing away from the diaphragm, the contactability of the electrode surface can be simplified, for example, in exemplary embodiments in which a positioning device is arranged in the recess of the piezoelectric element. Thus, in this embodiment, the electrode extends on both sides of the piezoelectric element. Preferably, the size of the surface of the connecting portion of the electrode extending on the side of the piezoelectric element facing away from the diaphragm is preferably less than 1 / 10 or 1 / 20 of the size of the electrode surface. Thus, the size of the electrode on the side of the piezoelectric element facing away from the diaphragm is preferably less than 1 / 10 or 1 / 20 of the size of the electrode on the side of the piezoelectric element facing the diaphragm. It has proven advantageous in this regard, on the one hand, that the working surface of the piezoelectric element is only slightly reduced, which is advantageous for the performance of the piezoelectric actuator, and on the other hand, that reliable contact of the electrode is also ensured.
[0057] The region of the connecting portion extending on the side of the piezoelectric element facing away from the diaphragm can be ring-shaped, in particular circular ring-shaped. The region can be collar-shaped. The region can be arranged around the recess of the piezoelectric element.
[0058] The electrically conductive adhesive can be arranged at least partially in the recess of the piezoelectric element. The electrically conductive adhesive can contact the connecting portion of the electrode. The electrically conductive adhesive can contact the region of the connecting portion extending on the side of the piezoelectric element facing away from the diaphragm.
[0059] Preferably, the electrically conductive adhesive connects components of the electrical connection, for example the connecting portion of the electrode or the electrical conductor, and for example the electrical line, in particular a flexible conductor, a printed circuit board or a contact element, to one another, in particular electrically and / or mechanically.
[0060] The same adhesive can be used both for the assembly adhesive joint for effectively connecting the piezoelectric actuator and the diaphragm and for the electrically conductive adhesive for the electrical connection. The electrical conductor can not only be contacted by the electrically conductive adhesive, but it can also be envisaged that it itself contains or is formed from the electrically conductive adhesive.
[0061] Preferably, the adhesive of the assembly adhesive joint and the electrically conductive adhesive are different adhesives. Preferably, the assembly adhesive joint comprises an adhesive whose strength and flexibility are coordinated such that the adhesive is strong enough on the one hand to transmit vibrations and flexible enough on the other hand to withstand the stresses acting on it due to the different coefficients of thermal expansion of the surrounding components.
[0062] The electrically conductive adhesive of the electrical connection can be softer or harder than the adhesive connecting the piezoelectric actuator to the diaphragm.
[0063] To adjust the thermal expansion coefficients of the diaphragm and the piezoelectric element, a compensating element, for example a compensating ceramic, is preferably arranged between the diaphragm and the piezoelectric actuator. By means of this usually disc-shaped compensating element, thermal expansion of the diaphragm can be absorbed and thus a voltage caused by thermal stress can largely be avoided. In particular, by means of this compensating element, mechanical stresses which can lead to a malfunction or breakage of the piezoelectric actuator can be prevented or reduced. The compensating ceramic can comprise a talc ceramic. Thereby the influence of the difference in thermal expansion between the piezoelectric element and the diaphragm can be attenuated. The compensating element is preferably electrically non-conductive. The engagement portion is preferably arranged between the piezoelectric actuator and the compensating element. The compensating element is preferably bonded to the diaphragm.
[0064] Preferably, the sensor comprises an additional electrical connection, which is preferably located between the additional electrode and the electronic system. Preferably, by means of the electronic system, a potential difference can be generated or intercepted between the electrode and the additional electrode. Preferably, by means of the electronic system, the electrode and the additional electrode, a potential difference can be applied or intercepted on opposite sides or surfaces of the piezoelectric element.
[0065] The surface of the piezoelectric element, which is separated from the piezoelectric element by the presence of the electrode and the additional electrode, can be referred to as the working surface of the piezoelectric element. Preferably, the working surface of the piezoelectric element is preferably greater than 7 / 10, 8 / 10 or 9 / 10 of the base surface of the piezoelectric element. The working surface is preferably rotationally symmetrical. The working surface can correspond to the surface of the additional electrode. The preferred rotational symmetry of the working surface can result in or contribute to the insensitivity of the piezoelectric actuator to rotation.
[0066] The additional electrode is preferably ring-shaped, in particular formed in the form of a circular ring. The additional electrode is preferably arranged around the recess. The additional electrode can extend at least almost over the entire side of the piezoelectric element facing away from the diaphragm, but preferably, in addition to an inner circular ring arranged around the recess, in order to form an insulating distance for isolating the additional electrode from the electrode. Preferably, the additional electrode is rotationally symmetrical about the same axis of rotation as the electrode. Preferably, the piezoelectric actuator has exactly two electrodes. Accordingly, the sensor preferably also only contains two electrical contact areas or contacts which are in contact with the electrodes of the piezoelectric actuator. The contact areas can contain solder connections and / or fusion connections. Preferably, they comprise adhesive joints using electrically conductive adhesive.
[0067] The sensor can comprise a positioning device for positioning the piezoelectric actuator and / or the compensating element relative to the diaphragm. The positioning device may, for example, comprise a (in particular cylindrical) punch on the side of the compensating element facing the piezoelectric actuator.
[0068] The two prongs of the vibration fork can be arranged on the diaphragm as a mechanical oscillator. The area of the vibration sensor, for example the piezoelectric actuator and the contact element, can be potted with a potting compound. Furthermore, a pin base can also be provided for the mechanical alignment and securing of the contact pins.
[0069] Preferably, the electrical contact is produced by means of an electrically conductive adhesive with the electrical conductor or the electrode. In this way or if the contact element is formed by an electrically conductive adhesive, an electrical connection between the electronic component and the electrode surface can be produced easily and reliably. The electrically conductive adhesive can be a silver conductive adhesive. The electrically conductive adhesive can have a thixotropy before it is cured. This means that the electrically conductive adhesive is not drawn into the recess by capillary action or only slightly. Thereby, any negative effects on the electrical connection between the electronic component and the electrode surface, which can be achieved by means of the electrically conductive adhesive, and the assembly of the adhesive joint can also be prevented or reduced.
[0070] Thus, the vibration sensor can comprise on the one hand an assembly adhesive joint and on the other hand an adhesive with an electrically conductive adhesive for contacting the piezoelectric actuator.
[0071] In an alternative embodiment, the electrical connection comprises or is formed by an inner conductor of a coaxial connection.
[0072] For example, the electrical connection can be realized as an inner conductor of a coaxial cable, wherein the inner conductor at least partially protrudes into the recess. Thus, the inner conductor of the coaxial cable can be offset by a length which approximately corresponds to the thickness of the piezoelectric element and inserted into the opening of the piezoelectric element. There, the inner conductor can be electrically connected with the electrode using an electrically conductive adhesive and at the same time be mechanically fixed. The adhesive and electrical contact can be made on the circumference of the inner conductor with the connection, but also at least partially by end face adhesive.
[0073] The inner conductor preferably penetrates at least half of the recess, more preferably at least 80%, particularly preferably almost completely. The greater the overlap between the inner conductor and the recess, the greater the surface that can be electrically and / or mechanically contacted. Thereby, a particularly good, stable electrical and / or mechanical connection can be achieved.
[0074] Preferably, the diameter of the inner conductor is adjusted to the diameter of the recess such that a defined distance between the inner conductor and the recess wall is maintained, which is bridged by the electrically conductive adhesive. For example, a calibration tool can be used for precise adjustment, with which the diameter of the inner conductor is machined during or after the offset such that it best fits in the recess.
[0075] In this embodiment, the closure element can be formed, for example, by the dielectric and / or the outer conductor of the coaxial connection.
[0076] The additional electrode can be contacted by the outer conductor of the coaxial connection. Also, the outer conductor can be electrically conductively bonded to the additional electrode, preferably at the end face.
[0077] In this way, a particularly easy-to-manufacture variant is provided, which effectively reduces the capillary effect of the recess.
[0078] In this way, the electrical and mechanical connection between the piezoelectric element and the supply line can be realized particularly easily and without additional components. BRIEF DESCRIPTION OF DRAWINGS
[0079] Further practical advantages and exemplary embodiments are further examined below in connection with the drawings.
[0080] Figure 1 schematically shows a sectional view of a part of a vibration sensor known from the prior art,
[0081] Figure 2 schematically shows a sectional view of a part of a first exemplary embodiment of a vibration sensor,
[0082] Figure 3 schematically shows a sectional view of a part of a second exemplary embodiment of a vibration sensor, Figure 2 an electrode of the vibration sensor shown,
[0083] Figure 4 schematically shows a perspective view of a piezoelectric actuator in Figure 2
[0084] Figure 5 schematically shows a perspective view of a piezoelectric actuator in Figure 2
[0085] Figure 6 schematically shows a sectional view of a part of a third exemplary embodiment of a vibration sensor,
[0086] Figure 7 schematically shows a sectional view of a part of a fourth exemplary embodiment of a vibration sensor,
[0087] Figure 8 schematically shows a sectional view of a part of a fifth exemplary embodiment of a vibration sensor,
[0088] Figure 9 schematically shows a perspective view of a piezoelectric actuator in
[0089] Figure 10 schematically shows a perspective view of a piezoelectric actuator in Figure 9
[0090] Figure 11 schematically shows a sectional view of a part of a fifth exemplary embodiment of a vibration sensor. DETAILED DESCRIPTION
[0091] Figure 1 schematically shows a sectional view of a part of a vibration sensor known from the prior art,
[0092] Here, the piezoelectric actuator 16 with the annular disk-shaped piezoelectric element 18 is bonded to an insulating compensating element 44 made of ceramic material. Likewise, the structure consisting of the piezoelectric actuator 16 and the compensating element 44 is fixed to the diaphragm 12 by means of an adhesive joint. The diaphragm 12 transitions to the housing 10 or is fastened thereto. By applying an electrical potential to the piezoelectric element 18, the diaphragm 12 can be set to vibrate in this structure. Other elements capable of mechanical vibration, such as a vibrating fork, can be placed on the outside of the diaphragm 12. Figure 1 The fork tines 62, 64 are only indicated by dashed lines. The side of the piezoelectric actuator facing the diaphragm is not freely accessible and therefore cannot be directly contacted.
[0093] Figure 2 The vibration sensor shown to some extent is used for detecting the filling level, the limit level or for monitoring process parameters and comprises a diaphragm 12 which can be set to vibrate. The diaphragm 12, the housing 10 and the tines 62, 64 can be as shown. Figure 1 As shown. Figures 2 to 5 In order to simplify the illustration, the diaphragm 12 is not shown.
[0094] The vibration sensor comprises a drive unit 14 designed as a piezoelectric actuator 16. The piezoelectric actuator has a piezoelectric element 18 and an electrode 20 connected to the piezoelectric element 18. The electrode 20 is a metallization layer of the piezoelectric element and has an electrode surface 21.
[0095] Furthermore, the vibration sensor comprises a bonding joint 26, more precisely a mounting bonding joint, by means of which the piezoelectric actuator 16 is effectively connected to the diaphragm 12, such that vibrations of the piezoelectric actuator 16 can be transmitted to the diaphragm 12 and vice versa. Furthermore, the vibration sensor comprises an electronic system 22 and an electrical connection 24 between the electronic system 22 and the electrode surface 21. Figure 2 Only the electrode surface 21 is shown as the lower boundary of the piezoelectric actuator 16 .
[0096] The piezoelectric element 18 has a groove 32, and the electrical connector 24 extends through the groove 32. The electrical connector 24 may also have an electrical wire 72, ie, a cable.
[0097] An electrical conductor 110 electrically connected to electrode surface 21 is arranged within recess 32. Electrical conductor 110 is part of electrical connector 24, located between electronics 22 and electrode surface 21, and comprises the connection portion 23 of electrode 20, more precisely, the metallization of the wall of recess 32. The vibration sensor also includes a closure element 125 for closing recess 32. This closure element 125 is arranged in recess 32 on the side 30 of piezoelectric element 18 facing away from diaphragm 12. Closing element 125 is designed as a contact element 130 bonded to piezoelectric actuator 16 and in electrical contact with electrical conductor 110. Contact element 130 is bonded into recess 32, among other things. Contact element 130 comprises a contact pin 140 and a conductive adhesive 40.
[0098] The sensor comprises a compensation element 44 in the form of a compensation ceramic between the diaphragm 12 and the piezoelectric actuator 16, with the adhesive joint 26 being arranged between the piezoelectric actuator 16 and the compensation element 44. The compensation element 44 itself is adhesively bonded to the diaphragm 12. Figure 2 As shown, the piezoelectric element extends in a plane 70 .
[0099] The adhesive joint 26 has a connection region 120 which is arranged in an annular manner around the recess 32 and in which it contacts the electrode surface 21 . Figure 2 In the exemplary embodiment shown, connection region 120 constitutes the entire bond joint 26, except for a smaller outer adhesive meniscus and inner adhesive meniscus 260. The bond joint has a constant thickness D within connection region 120. Although the diameter U of recess 32 is less than 2 mm, the adhesive used to assemble bond joint 26 is not drawn into recess 32 by capillary action and does not penetrate into recess 32, resulting in variations in the bond joint thickness and disrupting the formation of adhesive meniscus 260. Furthermore, the adhesive used to assemble the bond joint is prevented from disrupting the electrical contact of the metallization layer of the wall of recess 32.
[0100] This is Figure 2 In the exemplary embodiment shown, this is achieved because the recess 32 is closed by the contact element 130 surrounding the contact pin 140 and the adhesive joint 26 is produced, so that during the production of the adhesive joint 26 the air enclosed in the recess counteracts the capillary effect of the recess 32 . Figure 2 It is also shown that closing element 125 is arranged in recess 32 and on side 30 of the piezoelectric element facing away from diaphragm 12 .
[0101] Before assembly in the vibration sensor, i.e. before creating the adhesive joint 26, after introducing the recess 32, the piezoelectric element is metallized on one side and in the recess 32 to provide the electrode 20. By metallizing a region of the other side of the piezoelectric element, an additional electrode 45 is formed.
[0102] The contact pin 140 is glued into the recess 32 by means of the electrically conductive adhesive 40, closes the recess 32 and also makes electrical contact with the electrical conductor 110. The outer surface of the contact pin 140 arranged in the recess 32 is in electrical contact with the piezoelectric actuator 16, more precisely with the electrical conductor 110.
[0103] The outer dimensions of the contact pin 140 are complementary to the inner dimensions of the recess 32. In Figure 2 In the exemplary embodiment shown, the contact pin 140 has a collar 150 which is glued to the piezoelectric actuator 16.
[0104] As Figures 2 to 5 is shown, the piezoelectric element 18 has a first side 28 facing the diaphragm 12. The electrode surface 21 is arranged only on this first side 28. The piezoelectric element 18 has a second side 30 facing away from the diaphragm 12. The recess 32 extends through the center of the piezoelectric element 18 from the first side 28 to the second side 30.
[0105] The additional electrode 45 is arranged on the side 30 of the piezoelectric element 18 facing away from the diaphragm 12, and the vibration sensor comprises an additional contact element 190 (in the form of an additional contact pin 200) which is glued to the additional electrode 45. The additional contact pin 200 has a disc-shaped thickening 210 at the end.
[0106] The piezoelectric actuator 16 is formed as an adhesive annular disc 34 with a central covered contact 36. The piezoelectric element 18 and the electrode 20 are rotationally symmetrical about the same rotational axis.
[0107] In addition to the electrode surface 21, the electrode 20 also has a connection 23 Figure 3 ) which extends into the recess 32 and forms the electrical conductor 110.
[0108] The sensor comprises an additional electrical connection 74 between the additional electrode 45 and the electronic system 22. The additional electrode 45 has the shape of a circular ring 66, is arranged around the recess 32 and extends at least almost over the entire side of the piezoelectric element 18 facing away from the diaphragm 12, with the exception of an inner circular ring 68 arranged around the recess 32 for isolating the additional electrode 45 from the electrode 20.
[0109] Figure 3 The shape of the electrode 20 of the exemplary embodiment shown is illustrated, which has a flat circular ring-shaped electrode surface 21 and a connection 23. As Figure 2 is shown, the piezoelectric element 18 has a first side 28 facing the diaphragm 12. The electrode surface 21 is arranged only on this first side 28. The piezoelectric element 18 has a second side 30 facing away from the diaphragm 12. The recess 32 extends through the center of the piezoelectric element 18 from the first side 28 to the second side 30.
[0105] The additional electrode 45 is arranged on the side 30 of the piezoelectric element 18 facing away from the diaphragm 12, and the vibration sensor comprises an additional contact element 190 (in the form of an additional contact pin 200) which is glued to the additional electrode 45. The additional contact pin 200 has a disc-shaped thickening 210 at the end.
[0106] The piezoelectric actuator 16 is formed as an adhesive annular disc 34 with a central covered contact 36. The piezoelectric element 18 and the electrode 20 are rotationally symmetrical about the same rotational axis.
[0107] In addition to the electrode surface 21, the electrode 20 also has a connection 23 Figure 3 ) which extends into the recess 32 and forms the electrical conductor 110.
[0108] The sensor comprises an additional electrical connection 74 between the additional electrode 45 and the electronic system 22. The additional electrode 45 has the shape of a circular ring 66, is arranged around the recess 32 and extends at least almost over the entire side of the piezoelectric element 18 facing away from the diaphragm 12, with the exception of an inner circular ring 68 arranged around the recess 32 for isolating the additional electrode 45 from the electrode 20.
[0109] Figure 3 The shape of the electrode 20 of the exemplary embodiment shown is illustrated, which has a flat circular ring-shaped electrode surface 21 and a connection 23. AsFigure 2 and Figure 3 As shown in Fig. 2, the electrodes 20 extend on surfaces that are inclined with respect to each other, and in the exemplary embodiment shown in these figures, their shape consists of a circular surface with a hole, which forms the electrode surface 21, and a hollow cylinder adjoining the edge of the hole, which constitutes the connection 23. As shown in Fig. 2, the connection 23 can also have a region 42 that extends on the side 30 of the piezoelectric element facing away from the diaphragm. This region 42 is circular and also surrounds the recess 32 of the piezoelectric element 18. However, in all exemplary embodiments shown in Figs. 1 to 4, the connection 23 can be designed as an enlarged working surface of the piezoelectric element that does not have a region 42 extending on the side 30 of the piezoelectric element facing away from the diaphragm. Figures 2 to 5 As shown in Fig. 2, the connection 23 can also have a region 42 that extends on the side 30 of the piezoelectric element facing away from the diaphragm. This region 42 is circular and also surrounds the recess 32 of the piezoelectric element 18. However, in all exemplary embodiments shown in Figs. 1 to 4, the connection 23 can be designed as an enlarged working surface of the piezoelectric element that does not have a region 42 extending on the side 30 of the piezoelectric element facing away from the diaphragm. Figures 2 to 8 As shown in Fig. 2, the connection 23 can also have a region 42 that extends on the side 30 of the piezoelectric element facing away from the diaphragm. This region 42 is circular and also surrounds the recess 32 of the piezoelectric element 18. However, in all exemplary embodiments shown in Figs. 1 to 4, the connection 23 can be designed as an enlarged working surface of the piezoelectric element that does not have a region 42 extending on the side 30 of the piezoelectric element facing away from the diaphragm.
[0110] Figure 4 and Figure 5 A structure of the piezoelectric actuator 16 is shown, which has a circular piezoelectric element 18, electrodes 20 as described above, and a circular additional electrode 45.
[0111] Figures 6 to 8 Further exemplary embodiments are shown. Identical reference signs in this case denote identical elements with identical functions, unless stated otherwise. In this respect, reference is made to the above description. In the following, only differences to the exemplary embodiments shown in Figs. 1 to 4 are introduced. For the sake of clarity, Figure 2 Figures 6 to 8 the adhesive meniscus 260, which is present in all exemplary embodiments shown in Figs. 1 to 4, is omitted. Figures 6 to 8
[0112] Figure 6 An exemplary embodiment is shown in which the contact pins 140 and the additional contact pins 200 are part of a standardized electrical plug connection 160, and the distance 230 between the contact pins is the grid size. The contact pins 140 and the additional contact pins 200 serve as contacts for contacting the mating plug 220. Each contact pin has a recess in the form of a blind hole, which provides a sleeve portion of the respective contact pin for accommodating a mating plug contact. In this exemplary embodiment, the vibration sensor comprises the plug connection 160, which is bonded on the piezoelectric actuator 16, instead of flexible conductors. Figure 6 A potting cup 270 for introducing a potting compound (not shown in the figures) and a pin holder 280 for mechanically aligning and fixing the contact pins are also shown.
[0113] In Figure 7 and 8 In the exemplary embodiment shown, the vibration sensor comprises a printed circuit board 170 with electronic components 180. The contact element 130 electrically connects the piezoelectric actuator 16, more precisely the electrical conductor 110, to the printed circuit board 170 and also creates a fixed mechanical connection between the piezoelectric actuator 16 and the printed circuit board 170.
[0114] An electrical plug contact in the form of a 2-pin socket 240 is arranged on the printed circuit board 170.
[0115] In Figure 7 In the exemplary embodiment shown, one side of the contact element 130 contacts the piezoelectric actuator 16, in particular at least also the electrical conductor 110, via the electrically conductive adhesive 40, and the other side of the contact element 130 contacts the printed circuit board 170 directly or via the electrically conductive adhesive 40. Figure 7 The electrically conductive adhesive contacts the printed circuit board 170 at this point is not shown.
[0116] In Figure 8 In the exemplary embodiment shown, the contact element does not comprise a contact pin, but is formed by the electrically conductive adhesive 40, and the piezoelectric actuator 16 is electrically and mechanically connected to the printed circuit board 170 directly via the contact surface 250 of the printed circuit board.
[0117] If the connection portion 23 of the electrode has an area 42 that extends on the side 30 of the piezoelectric element facing away from the membrane 12, then, as Figure 8 is shown, the closure element 125 can be arranged only on the side 30 of the piezoelectric element facing away from the membrane 12. If the electrode does not have this area, then the electrically conductive adhesive 40 extends into the recess 32 and comes into contact with the metallized wall of the recess 32, which is different from Figure 8 as shown.
[0118] Figure 9 and Figure 10 A perspective view of a piezoelectric actuator 16 is shown, which can be used in other exemplary embodiments. In comparison with the piezoelectric actuator 16 shown in Figure 4 and Figure 5 In comparison with the variant of the piezoelectric actuator 16 shown in and
[0119] Figure 11 The cross-sectional enlargement in Figure 9 and Figure 10 shows a cross section of a further exemplary embodiment of a vibration sensor with a piezoelectric actuator 16 in the longitudinal direction of the recess 32.
[0120] In this exemplary embodiment, the electrical contacting of the piezoelectric element 18 is realized on the one hand by means of the inner conductor 86 of the coaxial line 84, which is arranged in the recess 32 of the piezoelectric element 18 and is electrically and mechanically connected to the piezoelectric element by means of the electrically conductive adhesive 40. The additional electrode 45 is connected to the outer conductor 88 of the coaxial line 84, which is also mechanically and electrically connected to the piezoelectric element by means of the electrically conductive adhesive 40.
[0121] By means of the embodiment shown, the electrical and mechanical contacting and sealing of the recess 32 can be realized particularly easily. Figure 11
[0122] Since the piezoelectric element 18 is constructed completely rotationally symmetrical by means of the central contact only, the stresses occurring as a result of the piezoelectric element deforming are less, which significantly increases the mechanical resilience and durability of the piezoelectric element 18. Furthermore, by eliminating the radially more outer contact points, the stiffness is also reduced, so that greater amplitudes can be produced.
[0123] List of reference signs
[0124] 10 housing
[0125] 12 diaphragm
[0126] 14 drive unit
[0127] 16 piezoelectric actuator
[0128] 18 piezoelectric element
[0129] 20 electrode
[0130] 21 electrode region
[0131] 22 electronics system
[0132] 23 connection of the electrode
[0133] 24 electrical connection
[0134] 26 adhesive joint
[0135] 28 side of the piezoelectric element facing the diaphragm
[0136] 30 side of the piezoelectric element facing away from the diaphragm
[0137] 32 recess of the piezoelectric element
[0138] 34 adhesive annular disk
[0139] 36 central cladding contact
[0140] 40 electrically conductive adhesive
[0141] 42 region of the connecting portion extending on the side of the piezoelectric element facing away from the diaphragm
[0142] 44 compensating element
[0143] 45 additional electrode
[0144] 62 tines
[0145] 64 tines
[0146] 66 circular ring
[0147] 68 inner circular ring
[0148] 70 flat surface
[0149] 72 electric line
[0150] 74 additional electrical connection
[0151] 84 coaxial line
[0152] 86 inner conductor
[0153] 88 outer conductor
[0154] 110 electric conductor
[0155] 120 connecting region of the adhesive joint
[0156] 125 closing element
[0157] 130 contact element
[0158] 140 contact pin
[0159] 150 collar
[0160] 160 electrical plug connection
[0161] 170 printed circuit board
[0162] 180 electronic component
[0163] 190 additional contact element
[0164] 200 additional contact pin
[0165] 210 thickening
[0166] 220 mating plug
[0167] 230 distance
[0168] 240 2-pin socket
[0169] 250 contact surface
[0170] 260 adhesive meniscus
[0171] 270 potting cup
[0172] 280 needle seat
[0173] D thickness
[0174] U diameter
Claims
1. A vibration sensor for detecting a fill level, a limit level or for monitoring a process parameter, comprising: - a diaphragm (12) which can be set into vibration; - a drive unit (14), wherein the drive unit (14) comprises a piezoelectric actuator (16) having a piezoelectric element (18) and electrodes (20) connected to the piezoelectric element (18), the electrodes having electrode surfaces (21); - an adhesive joint (26) by which the piezoelectric actuator (16) is effectively connected to the diaphragm (12) such that vibrations of the piezoelectric actuator (16) can be transmitted to the diaphragm (12); - an electronics system (22); - an electrical connection (24) between the electronics system (22) and the electrode surfaces (21); wherein the piezoelectric element (18) has a recess (32) and the electrical connection (24) extends through the recess (32), wherein an electrical conductor (110) which is electrically connected to the electrode surfaces (21) is arranged in the recess (32) and the vibration sensor has a closure element (125) for closing the recess (32).
2. The vibration sensor according to claim 1, characterized in that the closure element (125) is arranged at least also in the recess (32) and / or on a side (30) of the piezoelectric element (18) facing away from the diaphragm (12).
3. The vibration sensor according to claim 1 or 2, characterized in that the closure element (125) is designed as a contact element (130) and is in electrical contact with the electrical conductor (110).
4. The vibration sensor according to claim 3, characterized in that the contact element (130) is bonded on the piezoelectric actuator (16).
5. The vibration sensor according to claim 3 or 4, characterized in that the contact element (130) is bonded in the recess (32).
6. The vibration sensor according to any one of claims 3 to 5, characterized in that the contact element (130) comprises a contact pin (140).
7. The vibration sensor according to claim 6, characterized in that the contact pin (140) has a collar (150) which is bonded on the piezoelectric actuator (16).
8. The vibration sensor according to claim 6 or 7, characterized in that the contact pin (140) is part of an electrical plug connection (160).
9. The vibration sensor according to any one of claims 3 to 8, characterized in that the vibration sensor comprises a printed circuit board (170) having electronic components (180) and the contact element (130) electrically and mechanically connects the piezoelectric actuator (16) with the printed circuit board (170).
10. The vibration sensor according to any one of claims 3 to 9, characterized in that An additional electrode (45) is arranged on a side (30) of the piezoelectric element (18) facing away from the diaphragm (12), and the vibration sensor comprises an additional contact element (190) for making electrical contact with the additional electrode (45).
11. The vibration sensor according to claim 10, characterized in that the additional contact element (190) comprises an additional contact pin (200) glued on the additional electrode (45).
12. The vibration sensor according to claim 11, characterized in that the additional contact pin (200) is at a distance (230) from the contact pin (140) corresponding to a grid size.
13. The vibration sensor according to any one of claims 1 to 6, characterized in that the electrical connection is formed by an inner conductor (86) of a coaxial connection.
14. The vibration sensor according to claim 13, characterized in that the closing element is formed by a dielectric and / or outer conductor (88) of the coaxial connection.