WO2018073031A1

WO2018073031A1 - Connecting element having an integrated sensor

Info

Publication number: WO2018073031A1
Application number: PCT/EP2017/075600
Authority: WO
Inventors: Matthias BRENNEIS
Original assignee: GLBS Patentverwertungsgesellschaft GbR
Priority date: 2016-10-21
Filing date: 2017-10-09
Publication date: 2018-04-26
Also published as: CN109844478A; JP6728492B2; KR20190072581A; KR102234823B1; JP2019536014A; CN109844478B; DE102016012564A1

Abstract

The present invention relates to a connecting element (10) having a longitudinally extended connecting body (11) and a sensor (12), and to a method and measuring system provided with such a connecting element (10). The connecting element (10) has a longitudinally extended connecting body (11) and a sensor (12) which is arranged in a hollow space (14) of the connecting body (11) and is firmly connected with the connecting body (11), wherein the sensor (12) has at least one sensor element (22, 24) with a load-dependent modulus of elasticity which changes as a function of an acting mechanical force, and wherein the sensor element (22, 24) can be coupled with a measuring arrangement (30) in a signal-transmitting manner.

Description

Connecting element with integrated sensor

Description

The present invention relates to a connecting element with a

elongated connecting body and with a sensor which is arranged in a cavity of the connecting body and fixedly connected to the connecting body. In particular, the invention relates to a force measuring bolt, wherein the bolt also acts as a connecting element for components to be joined together. In a further aspect, the invention relates to a measuring system with a measuring arrangement and with a connecting element and to a method for measuring a mechanical force acting on a connecting element.

background

Connecting elements with integrated sensor devices, such as force measuring pins are known in the art, such as from

WO 2013/139464 A1. There is proposed a structure that is in the

Essentially consists of a longitudinally oriented support structure and a sensor unit. For the sensor unit there is the application of strain gauges proposed to a carrier. The sensor unit is designed for detecting mechanical and / or thermal measured variables.

In contrast, the present invention has for its object to provide an improved connection element and an improved measuring system and an improved method for measuring a force acting on a connecting element, by means of which a long-term stable and

particularly precise measurement of a force acting on the connecting element mechanical force can take place. The connecting element should be characterized by a well reproducible structure. The measuring system and the

Measuring methods should also be characterized by high precision and a high degree of reproducibility.

Advantageous embodiments

This object is achieved with a connecting element according to the independent claim 1 and with a measuring system according to claim 8 and with a method according to claim 14. Advantageous embodiments are each the subject of dependent claims.

Accordingly, according to one aspect, a connecting element with a

elongated connecting body and provided with a sensor. The sensor is arranged in a cavity of the connecting body. The sensor is also firmly connected to the connecting body. The sensor has at least one

Sensor element with a load-dependent modulus of elasticity. This means that the modulus of elasticity of the material of the sensor element changes as a function of a mechanical force acting on the sensor element.

The sensor element can also be coupled with a measuring arrangement in a signal-transmitting manner. The sensor element is preferably an electrical one

Sensor element, which is electrically signal transmitting with the measuring arrangement coupled. The coupling can be wired or wireless. The sensor is typically in a blind hole designed cavity of the connecting body. The cavity can be introduced in particular as an axial bore in the connecting body. Of the

Connecting body may in particular have the form of an elongated screw or an elongated cylindrical bolt.

Typically, the connecting body has at least one

External thread section and / or a radially widened head portion. The connecting body, thus the entire connecting element can be used for example as a connecting screw or as a connecting bolt to connect at least two components together.

The load-dependent elastic modulus of the sensor element gives the

Sensor element a natural vibration frequency, which varies depending on the prevailing mechanical load. Typically that is

Sensor element excited by means of an oscillating electrical input signal to mechanical vibrations. A resonant or natural frequency of the at least one sensor element is due to the load-dependent

Modulus of elasticity as a function of the momentarily on the sensor element

modifiable mechanical force.

By means of the measuring arrangement is typically the natural vibration frequency of the sensor element, e.g. according to an impedance-reflection measurement method

can be determined metrologically. From a measured natural vibration frequency can be directly inferred about the height of the currently on the

Pull sensor element acting mechanical force.

In this case, it is of particular advantage that the oscillation natural frequency of the at least one sensor element changes largely exclusively by a change in the mechanical force acting on the sensor element. Over a long period repeated measurements to be performed on the

Sensor element acting force therefore always lead to consistent

Results. In this way, a particularly long-term stable and precise measurement of the force acting on the sensor element mechanical force allows.

The fact that the sensor and its sensor element is located in a cavity of the connecting body and in that the sensor and its sensor element are firmly connected to the connecting body, the sensor element is quasi in the load path of the connecting element, thus in the load path of

Connecting body. The sensor element is thus exposed to the same extent as the connecting body itself a mechanical stress or a mechanical force. The feasible with the connecting element measuring method requires the embedding of the at least one sensor element in the load path or in the power flow of the connecting body. In this way, changes in the mechanical force acting on the at least one sensor element can be directly transferred into a change in the natural vibration frequency of the at least one sensor element which can be measured by means of the measuring arrangement.

Given an appropriate calibration or calibration, an electrically measurable oscillation natural frequency of the at least one sensor element is a direct quantitative measure of the mechanical force acting on the at least one sensor element and thus also on the connecting body.

According to a further embodiment, the sensor has a first sensor section and a second sensor section. First and second sensor sections are spaced apart in the longitudinal direction of the connecting body, typically also in the longitudinal direction of the cavity. The first sensor section and the second sensor section are each firmly connected to the connecting body or they are fixed thereto. The first sensor section and the second sensor section can at the same time also represent end sections of the sensor with respect to the longitudinal direction of the connecting body or with corresponding longitudinal ends

coincide. However, it is also conceivable that only one of the first and second sensor section coincides with a longitudinal end of the sensor. By virtue of the fact that both the first and the second sensor section are spaced apart in the longitudinal direction and are respectively connected directly or indirectly to the connecting body and fixed accordingly to the connecting body, any mechanical stresses acting on the connecting body in the longitudinal direction can be correspondingly transmitted to the sensor. By this type of arrangement and fixation of the sensor in the cavity, the sensor is, so to speak, in a power flow of the connecting body, while the connecting body itself represents the actual main power flow. A force acting on the connecting body mechanical stress or force in the longitudinal direction is due to the respective connection of the first and second sensor portion with the

Transfer connecting body to the first and second sensor sections accordingly.

In accordance with a further embodiment, the at least one sensor element has an electrically measurable natural vibration frequency that is variable as a function of a mechanical force. This property of the sensor element makes use of the measuring arrangement. By means of the measuring arrangement, the at least one sensor element of the sensor can be excited to mechanical vibrations. According to the momentarily acting on the sensor element mechanical force by means of the measuring arrangement, the respective

Natural vibration frequency of the sensor element as a characteristic characteristic of the same measurable. The natural vibration frequency is a direct measure of the mechanical force currently acting on the relevant sensor element.

According to a further embodiment, the at least one sensor element comprises a piezoelectric crystal or a piezoelectric ceramic. The

Sensor element may also consist of one or more piezoelectric crystals or of one or more piezoelectric ceramics. When implementing the at least one sensor element as a piezoelectric ceramic, this can be, for example, a lead zirconate titanate and / or a lead magnesium Niobate or other, suitable for the production of piezoelectric ceramics materials.

Although piezoelectric crystals or piezoelectric ceramics are far too rigid or inelastic, they still have a load-dependent

Elastic modulus on.

In this case, provision is made in particular for the at least one sensor element to be electrically contacted in the longitudinal direction and for a polarization direction of the piezoelectric crystal or the piezoelectric ceramic to be aligned essentially parallel to the longitudinal direction of the connecting body. By such an orientation and alignment is achieved that the piezoelectric crystal or the piezoelectric ceramic of the at least one sensor element in the longitudinal direction, that is in the longitudinal direction of the connecting body to

Vibrations according to the piezoelectric longitudinal or longitudinal effect can be excited. In this way, the at least one sensor element for measuring and determining is preferably one in the longitudinal direction of the

Joint body acting mechanical force trained. According to a further embodiment, an electrical contact which can be electrically conductively connected to the measuring arrangement is arranged at one longitudinal end of the at least one

Sensor element arranged. The electrical contact on, for example, a proximal longitudinal end of the sensor element is connected to the measuring arrangement, while an opposite distal end of the sensor element can be connected, for example, in an electrically conductive manner to the connecting body. Of the

Connecting body may represent a ground potential, while the electrical contact at the proximal end of the sensor element is preferably electrically insulated from the connecting body. By means of a single electrical contact, the sensor element to

Vibrations are stimulated. According to the measuring system designed in reflection arrangement or a corresponding measuring arrangement, a reaction, thus a reflection response of the at least one sensor element with the same electrical contact and transmitted to the measuring device. A single signal transmission cable or a single signal transmitting

Connection or coupling between the measuring arrangement and the at least one sensor element is therefore sufficient in principle to carry out a force measurement.

According to a further embodiment, the sensor has at least two in

Longitudinal direction of the connecting body spaced apart sensor elements, between which an electrical contact is arranged. This is in electrical contact with both sensor elements. It is almost a one

Series connection of two sensor elements. By means of, based on the longitudinal direction or axial direction between the sensor elements located electrical

Contact both sensor elements can be excited simultaneously to vibrations. The electrical contact can also act as a sensor to determine the vibration natural frequencies of the sensor elements. The two sensor elements are due to their respective arrangement and fixation in the cavity of the connecting body widely exposed identical, acting in the longitudinal direction mechanical forces. Your load-dependent

Modulus of elasticity consequently alters equally as a result of a change in the external force.

By means of at least two sensor elements spaced apart from one another in the longitudinal direction and separated from one another by an electrical contact, larger signal amplitudes at the electrical contact can be measured. The sensitivity and measuring accuracy can be increased thereby.

According to a further embodiment, the sensor is exposed within the cavity of a mechanical compression in the longitudinal direction. Thus, the sensor can be biased in the longitudinal direction. In a primal or initial state of the

Connecting element is subject to the sensor element thus an axial

compressive bias. When used as intended

Connecting element act on this axial tensile forces. These counteract the bias of the sensor element. The measure of a measurable through this Displacement of the natural vibration frequency of the at least one sensor element is insofar a direct measure of the force acting on the connecting body mechanical force in the longitudinal direction. According to a further aspect, a measuring system is provided which has at least one previously described connecting element and which at least one

Measuring arrangement, typically in the form of a measuring device. The

Measuring arrangement or the measuring device can be signal-transmitting coupled to the at least one sensor element of the sensor of the connecting element. The

signal-transmitting coupling can be implemented in particular wired, but also wirelessly. The measuring arrangement is designed to determine the electrically measurable natural vibration frequency of the at least one sensor element of the sensor of the connecting element. From the measurable

Natural vibration frequency is then in the longitudinal direction of the

Connecting body, thus acting on the connecting element mechanical force derivable.

According to a development, the measuring arrangement of the measuring system has at least one electrical signal generator for generating a temporally varying electrical input signal. The electrical input signal is typically an oscillating, possibly periodically oscillating electrical signal. The

Measuring arrangement further comprises at least a first signal receiver. The first signal receiver and the signal generator are connected to the at least one

Sensor element of the sensor of the connecting element coupled. During operation of the measuring system, the first signal receiver and the signal generator are electrically connected to the at least one sensor element. The first signal receiver is further designed to evaluate a response signal of the at least one sensor element in response to the input signal. In this case, it is provided in particular that the signal generator generates a sequence of input signals of different frequency and that the signal receiver determines and determines a signal amplitude of the response signal as a function of the frequency of the respectively associated input signal. In this way are by means of the signal generator and by means of the signal receiver the

Oscillation natural frequency of the at least one sensor element determinable.

It is further provided that the sensor element as a component of a

Assembly composite is configured. The Montageverbund can next to the

Sensor element still have a mounting cap or a functional component. The mounting cap and / or the functional component may be non-positively coupled to the at least one sensor element. In particular, the at least one sensor element can axially on at least one of mounting cap and

Abut functional component. It can also be arranged axially between the mounting cap and the functional component clamping inside the cavity.

That of the sensor element and at least one of functional component and

Mounting cap formed assembly may have a natural vibration frequency in the range between 1 kHz and 500 kHz or e.g. between 10 kHz and 100 kHz. This area is metrologically very good and measurable with inexpensive to implement measuring instruments. Thus, instead of or in addition to determining a natural vibration frequency of the sensor element, the corresponding natural vibration frequency of the assembly of

Sensor element with the functional component and / or measured with the mounting cap and determined.

A signal-transmitting coupling between the at least one sensor element and the measuring arrangement typically takes place by means of a signal cable. In this respect, the signal cable provides a wired signal-transmitting connection between the sensor element and the measuring arrangement. The connection of the signal cable with the sensor element and / or with the measuring arrangement can be designed as a detachable plug connection with a plug and with a socket corresponding thereto. The connection may also have one or more spring contacts and / or a contact plate.

According to a further embodiment, the signal generator and the first

Signal receiver via a common signal cable with the at least one Coupled sensor element. It is specifically intended that the

Measuring arrangement for performing an impedance reflection measurement is configured. The input signal for vibration excitation of at least one

Sensor element as well as a quasi-reflected from the first sensor element

Response signal is transferable via one and the same signal cable between the signal generator, the signal receiver and the sensor element. The use of only a single signal cable proves to be advantageous in terms of assembly technology and manufacturing technology for the connecting element. According to a further embodiment of the measuring system is provided that the

Signal generator and the first signal receiver are connected in series via an electrical resistor. The first signal receiver is furthermore directly electrically connected to the at least one sensor element. An electrical

Connection path between the signal generator and the at least one

Sensor element runs equally through the electrical resistance. By means of the electrical resistance are the signal generator and the first

Signal receiver virtually decoupled from each other. The proportion of the input signal can thereby be reduced or attenuated at the first signal receiver. Similarly, the proportion of the response signal on the part of the signal generator can be reduced or attenuated.

It is further provided according to a further embodiment that the

Measuring arrangement next to the first signal receiver nor a second

Signal receiver, which for measuring a frequency of the

Signal generator generated output signal is formed. The second

Signal receiver can be switched almost parallel to the signal generator. It can be on the same side of the electrical resistance as the signal generator. By means of the second signal receiver can actually from the

Signal Generator generated frequency of the input signal can be measured precisely. Consequently, only the measurement signals of the first and second signal receivers are to be compared with one another for signal evaluation. According to a further embodiment, the first signal receiver is designed to measure a frequency spectrum of the response signal of the at least one sensor element. Likewise, the second signal receiver can also be designed to measure a frequency spectrum of the input signal generated by the signal generator. At least one of the first and second signal receiver can be equipped with an evaluation unit or signal-transmitting coupled to an external evaluation unit, which is configured to

Natural vibration frequency of the excited with the input signal

Quantify sensor element.

According to a further aspect, a method for measuring a force acting on a connecting element is further provided. The method comprises the steps of providing a previously described connecting element and electrically connecting the at least one sensor element of the

Connecting element with a measuring arrangement, typically with a measurement arrangement associated with the measuring system described above. The method further comprises applying the at least one sensor element with a time-varying electrical signal. Typically this will be at least one

Sensor element subjected to an oscillating electrical input signal of variable frequency.

The method further comprises measuring one of at least one

Sensor element reflected response signal and the evaluation of the response signal for determining a force acting in the longitudinal direction of the connecting element or on the sensor element force. The method is in particular carried out computer-aided. In that regard, the steps of loading the at least one sensor element with the time-varying electrical signal, measuring the reflected response signal and evaluating the

Response signal computer implemented, in particular software implemented

be designed.

The measuring arrangement typically has at least one processor, such as a microprocessor or microcontroller and a memory. The measuring arrangement may further comprise a programmable logic controller and / or an FPGA module (Field Programmable Gate Array). The measuring arrangement can be designed as a computer or as a tablet computer. The measuring method described can be carried out in particular with a previously described measuring system, or at least with a connecting element described above. In that regard, all mentioned in relation to the connecting element and the measuring system features, properties and advantages also apply equally to the measuring method; and vice versa.

According to a further embodiment of the measuring method, the evaluation of the response signal comprises a spectral analysis of the response signal. To determine the longitudinal direction of the connecting element or on the at least one

Sensor element acting force is a resonance or

Natural vibration frequency of the at least one sensor element measured. Due to the load-dependent modulus of elasticity of the at least one sensor element, the resonant or natural vibration frequency of the at least one sensor element is a direct measure of the force acting in the longitudinal direction on the sensor element and on the elongated connecting body.

Of course, the method may also include a calibration and / or calibration of the connecting element used before the measurement is carried out. In this way, any measurable natural vibration frequency can be determined in accordance with a preliminary characterization of the

Connecting element to be assigned a mechanical force. When using the measuring method, the previously stored for example in a memory

To read assignments of natural vibration frequencies and hereby associated mechanical forces only after measuring a natural vibration frequency.

Brief description of the figures Further advantages, features and advantageous properties of

Connecting element, the measuring system and the hereby feasible

Measuring method are described in the following description of

Embodiments explained with reference to the figures. Hereby show:

1 is a schematic representation of a cross section through a connecting element connecting two components, a cross section corresponding to FIG. 1, but with a slightly different configuration of the connecting element, a schematic enlarged representation of the fixation of a sensor in the cavity of the elongated connecting body according to a first embodiment , a further embodiment for fixing the sensor in the cavity, a further embodiment for fixing the sensor in the cavity, a schematic representation of an embodiment of the sensor with two sensor elements,

Fig. 7 shows a further embodiment of a sensor with a total of two

Sensor elements,

8 shows a schematic representation of a measuring arrangement to be signal-connected to the sensor,

9 is a diagram of a measurement in the presence of a first force,

10 is a diagram of a force measurement in the presence of a second force, 1 1 is a diagram with a total of four plots of measured natural vibration frequencies at different prevailing forces, and FIG. 12 is a flowchart of the measuring method.

Detailed description

A measuring system for measuring and determining a force acting on a connecting element 10 in the axial or longitudinal direction is shown schematically in FIGS. 1 and 2. The measuring system 50 comprises a connecting element 10 with an elongated connecting body 11 and a measuring arrangement 30, which is typically configured in the form of a measuring device. The connecting element 10 is designed as a force measuring pin. The elongated connecting body 1 1 has a helical or bolt-like elongated cylindrical shape.

In the embodiment of Fig. 1, the connecting body 1 1 a

elongate shaft 17 with a arranged on an upper shaft end radially widened head 18. The shaft 17 has, at least in sections, an external thread 25, which is designed in a corresponding thereto

Internal thread 29 of a first component 1 is screwed or screwed into this. The first component 1 has in the present embodiment a

Through opening 3, which is arranged in alignment with a passage opening 4 of a second component. The shaft 17 passes through the passage opening 4 of the second component 2. The radially widened head 18 is axially in an abutment position with an opening facing away from the first component opening boundary of the through hole 4.

By screwing the connecting body 1 1, the connecting element 10 can apply a the first and the second component zusammenfügende force. Consequently, by means of the connecting element 10, the second component 2 is clamped between the head 18 and the first component 1. To screw in the

Connecting element 10 in the first component 1, the head 18, for example, have a radially outer key surface. Alternatively, and as shown in Fig. 1, an end face of the head 18 a

Receiving 28, with one with a screwing

corresponding positive locking structure 27, or provided with a key surface. The screwing of the connecting element 10 and the application of a tightening torque is with the generation of a longitudinal or

Axially aligned mechanical stress through the connecting body 1 1 accompanied. By screwing and screwing the connecting element 10, the connecting body 1 1 undergoes a tensile stress in the longitudinal or axial direction.

The connecting body 1 1 has in the present embodiment radially centrally a longitudinally extending cavity 14, which in

Axial direction up to the end face of the head 18 opens. The cavity may be configured as a kind of axial blind hole in the connecting body 1 1. In the cavity 14, a sensor 12 is fixed. The sensor 12 has, as shown in more detail in FIGS. 3 to 7, at least one sensor element 22, possibly also two sensor elements 22, 24. The at least one sensor element 22, possibly also both sensor elements 22, 24 have a material with a load-dependent modulus of elasticity.

The material of the sensor element 22 changes its elasticity or rigidity depending on the respective prevailing mechanical force. The change in the modulus of elasticity is reflected in particular in the vibration behavior of the

Sensor element 22, 24 down. The natural vibration frequency of the sensor element 22, 24 at an electrical or electromechanical, for example

Vibration excitation changes depending on the momentarily acting on the sensor element 22, 24 mechanical force or voltage. An oscillation natural frequency of the at least one sensor element 22, 24 can be measured by means of the measuring arrangement 30 and the signal-transmitting electrical coupling formed, for example, by means of a signal cable 36, between the sensor 12 and the measuring arrangement 30. For determining the natural vibration frequency of the at least one

Sensor element 22, 24, the implementation of an impedance reflection measurement is provided. That is, via the signal line 36, the at least one

Sensor element 22, 24 excited to mechanical vibrations. One

Reflection signal as a response signal is then equally transmitted from the signal cable 36 to the measuring device 30. By means of a tuning through a predetermined frequency band is in this way the

Vibration natural frequency of the sensor 12 under mechanical tension can be determined.

The construction of the measuring system 50 according to FIG. 2 is analogous to the design of the

Measuring system according to FIG. 1. Here, however, in contrast to the embodiment of FIG. 1 instead of a provided with a head connector body 1 1 a in

Substantially completely cylindrical connecting body 1 1 1 is provided which has an external thread 25, 45 at opposite end portions. The side facing away from the first component 1 side of the second component. 2

projecting end of the connecting body 1 1 1 is present with a

External thread 45 is provided, which with an internal thread 46 a

Nut 42 cooperates. The nut 42 has at her

Outer circumference of a positive locking structure 47, by means of which, with the aid of a suitable screwing a torque on the nut 42 can be applied.

The cavity 14 for the sensor 12 is also provided here as a cylindrical blind hole radially centered in the connecting body 1 1 1.

In Figs. 3 to 5 are different embodiments for fixing and

Holder of the sensor 12 shown within the cavity 14. The sensor 12, which is shown in FIGS. 3 to 5 as a monolithic sensor, may have a single sensor element 22, for example in the form of a piezoelectric crystal or in the form of a piezoelectric ceramic. However, the sensor 12 may have two or more sensor elements 22, 24, as shown by way of example in FIGS. 6 and 7. The sensor 12 is electrically contacted with its opposite longitudinal ends. A lower end of the sensor 12, which is located on a bottom 60 of the cavity 14, is directly electrically conductive with the bottom 60 and thus with the typically made of a metal

Connecting body 1 1 contacted. An opposite end of the sensor 12 communicates with an electrical contact 26. The electrical contact 26 is electrically connected to the measuring arrangement 30 via a signal cable 36. The sensor 12 is fixed within the cavity 14 by means of a mounting cap 64. Between the mounting cap 64, which may also be made of metal and the electrical contact 26, an electrical insulator 66 is further arranged. In this way, the electrical contact 26 is electrically insulated from the metallic connecting body 1 1. The mounting cap 64 has a

Cable gland 65 on. The electrical insulator 66 likewise has a cable feedthrough 67. Thus, the signal cable 36 can be passed through the mounting cap 64 and through the electrical insulation 66.

For the mechanical fixation of the sensor 12 within the cavity 14 in the present case a plastic deformation of the connecting body 1 1 is provided. Manufacturing technology can be introduced into an initially hollow cylindrical cavity 14 of the sensor 12 together with the electrical contact 26, 27, the signal cable 36 and the electrical insulator 66 and the mounting cap 64. Then there is a radially inwardly directed deformation of the inner wall 62 of the cavity 14 such that the mounting cap 64 and thus on the entire assembly of mounting cap 64, electrical insulator 66 and sensor 12 exerts a biasing force acting in the axial or longitudinal direction. In other words, the sensor 12 in the axial direction or the longitudinal direction of the

Connecting body 1 1 compressed. After the plastic deformation has taken place, the inner wall 62 has at least one or more radially inwardly projecting projections 63, which keep the sensor 12 fixed in the cavity 14 under prestress. In mechanical terms, the sensor 12 is compressed in the axial direction between the bottom 60 and at least one radially inwardly projecting projection 63, which may also be configured annularly. As a result, a first sensor portion 15 and a second sensor portion 1 6, which are spaced from each other with respect to the longitudinal direction of the connecting body 1 1, respectively separately connected to the connecting body 1 1 and fixed thereto. The second sensor section 16, which in the present embodiment with a

Longitudinal end of the sensor 12 coincides, is located in the immediate

Anlagestellung with the bottom 60 of the cavity 14. The first sensor section 15, which coincides with the opposite longitudinal end of the sensor 12, is located in immediate abutment position to the electrical insulator 66 or the mounting cap 64th

The first sensor section 15 is so far on the mounting cap 64 and the electrical insulator 66 indirectly fixed to a longitudinally spaced from the bottom 60 of the connecting body 1 1, for example with the

Tab 63 connected or fixed thereto. An acting in the longitudinal direction or axial direction of the connecting body 1 1 force, such as a tensile load on the connecting body 1 1 has an immediate effect on the axial

Compression of the sensor 12. A tensile load on the connecting body 1 1 counteracts in particular the bias of the sensor 12. This inevitably leads to a change in the axial and longitudinal mechanical force acting on the sensor 12. As a result, the sensor 12 or its sensor element 22, 24 changes its electrically measurable

Natural oscillation frequency. The change in the natural vibration frequency is thus an immediate measure and an indication of a change in the

Connecting body 1 1 acting tensile stress.

In the embodiment according to FIG. 4, instead of a plastic deformation of the inner wall 62 of the cavity 14, a frictional holding of the arrangement of sensor 12, electrical insulator 66 and mounting cap 64 is provided. Instead of a plastic deformation for generating a radially inwardly projecting projection 63 of the inner wall 62 is according to the embodiment of FIG. 4 a cohesive connection of the mounting cap 64 and the inner wall 62 is provided. This can be done for example by welding and to form welds 1 63. The cohesive connection of mounting cap 64 and inner wall 62 also takes place here under axial compression of the sensor 12.

The further embodiment of FIG. 5 provides, instead of a cohesive connection, to screw the mounting cap 64 into the cavity 14 and fix it quasi by means of a screw connection mi cavity 14. For this purpose, the mounting cap 64 has on its outer side an external thread 165 which can be brought into engagement with an internal thread 1 66 provided on the inner wall 62. Similar to the head 18 according to FIG. 1, the sensor also has the same here

facing away from the end cap 64 has a form-fitting structure for a torque-transmitting coupling with a screwing on. Hereby, the mounting body 64 can be screwed into the cavity 14 to produce an axial compression acting on the sensor 12.

In the exemplary embodiments according to FIGS. 6 and 7, two sensor variants 12 are shown, in which the sensor 12 has two sensor elements 22, 24 connected in series instead of one single sensor element 22. The sensors 12 according to FIGS. 6 and 7 can be fixed under bias in the cavity 14 according to one of the methods described in FIGS. 3 to 5, without this being explained in more detail with reference to FIGS. 6 or 7.

As shown in Fig. 6, is located between a first sensor element 22 and a second sensor element 24, the electrical contact 26, which with the

Signal cable 36 is electrically connected. In that regard, the first sensor element 22 on an axial cable gland 23. Similar to FIGS. 3 to 5, the mounting cap 64 also causes the sensor 12 with its two sensor elements 22, 24 to be fixed in the cavity 14 under an axial prestress, in particular under an axial compression. The first sensor element 22 and the second sensor element 24 are separated from each other in the longitudinal direction of the connecting body 1 1 and in the longitudinal direction of the cavity 14 by the electrical contact 26. As a result of the simultaneous electrical contacting with the electrical contact 26, the first sensor element 22 and the second sensor element 24 can be acted upon in an identical manner by an oscillating input signal. As a result of

mechanical series connection of first and second sensor element 22, 24 and the fact that the first and the second sensor element 22, 24 axially axially adjacent to each other in the cavity 14 are axially biased by the mounting cap 64, they are also far-reaching same mechanical compressive stresses in the longitudinal direction. Consequently, the answer is also the

Sensor elements 22, 24 far-reaching identical, so that the

Vibration eigenfrequencies of first sensor element 22 and second

Sensor element 24 can be recorded with one and the same electrical contact 26 and supplied via the signal cable 36 of the measuring device 30. The electrical contact 26 facing away from the longitudinal ends of the first

Sensor element 22 and second sensor element 24 are electrically connected to the

Mounting cap 64 and connected to the bottom 60 of the cavity 14. They can both be at ground potential, so to speak. In the further embodiment according to FIG. 7, in addition to the construction according to FIG. 6, a further functional component 68 is arranged between the second sensor element 24 and the bottom 60 of the cavity 14. The functional component 68 may have a defined elasticity or rigidity and thus have a far-reaching influence on the overall elasticity of the structure of the sensor 12. From a mechanical point of view and with regard to a tensile or compressive load, the mounting cap 64, the first

Sensor element 22, the electrical contact 26, the second sensor element 24 and the functional component 68 quasi connected in series.

By suitable choice of a functional component 68 with variable elasticity or

Geometry can be the type of mechanical coupling between the

Connecting body 1 1 and the sensor 12 are adapted to different measurement requirements. In particular, by selecting a functional component 68 from a number of available functional components with different elastic properties or geometries on the sensitivity of the sensor

Modification of mechanical stresses and mechanical loads of the connecting body 1 1 are variably adjusted. Finally, FIG. 8 schematically shows the structure of the measuring arrangement 30. On the output side and via a signal cable 36, the measuring arrangement 30 can be coupled with the sensor 12 in a signal-transmitting manner. The measuring arrangement 30 has a

Signal generator 32 and a first signal receiver 34 and a second signal receiver 35. Between the first signal receiver 34 and the second signal receiver 35, an ohmic or electrical resistance 38 is arranged, which is essentially for a decoupling of input signals and

Provides response signals. The second signal receiver 35 is primarily used for monitoring and frequency measurement of the input signals generated by the signal generator 32. The input signals are from the first

Signal receiver 34 due to the resistor 38 only reduced or

measured with attenuation. The first signal receiver 34, however, is directly connected to the signal cable 36, thus with the output or input of the after

Reflection method working measuring device 30 coupled. The response signals, which are reflected by the sensor 12 and characterize the natural vibration frequency of the sensor 12, are primarily from the first

Signal receiver 34 received. Due to the resistor 38, the reflected response signals of the sensor 12 in the second signal receiver 35 are received only reduced or attenuated.

In operation, the measuring arrangement 30 and the entire measuring system 50 is

provided, the frequency of the input signal over a predetermined

Frequency range to tune to find that vibration frequency at which the sensor 12 its resonance or his

Having natural vibration frequency.

In the illustration of two diagrams in FIGS. 9 and 10, the amplitude A of a signal for two different elements acting on the connecting element 10 is shown axial forces F1 and F2 shown. At the force F1 is the

Vibration natural frequency of the sensor 12 and its sensor element 22, 24 at a frequency f1. When a force F2 is applied, the natural vibration frequency, as shown in FIG. 10, is at a frequency f2. The frequency f1 is greater than the frequency f2. Consequently, the force acting in total on the sensor 12 is less in the example of FIG. 10 than in FIG. 9.

In view of the fact that the external force acting on the connecting element 10 or externally applied force, and thus the via the connecting element 10 to the components 1, 2 to be transmitted tensile force of the bias of the sensor 12th

is opposite, the configuration of FIG. 10 may represent a force F2 which is greater than the force F1 of FIG. 9. Thus, the force F1 can represent an unloaded initial situation of the connection arrangement 10, in which the

Sensor element 22, 24 or one of sensor element 22, mounting cap 64 and / or functional component 68 formed assembly composite is arranged with an axial bias in the cavity 14 is fixed. One by tightening one

Screw connection generated tensile force on the connecting element 10 counteracts the original biasing force. The total burden on the

Sensor element 22 and / or on the assembly composite is thereby reduced. As a result, the natural vibration frequency decreases from f1 to f2. Such a dependency can be observed in particular with a progressive dependence of the modulus of elasticity on an applied force. With a degressive dependence of the modulus of elasticity on an applied force, the frequency would increase in the previously described scenario.

In the diagram according to FIG. 11, a total of four measurements are included

represented different forces applied to the connecting element. The individual graphs reflect forces or torques from 0 to 60 kN. The dashed diagram corresponds to a connector in the original state, the dashed line represents a measurement at a force of 20 kN. The diamond chart represents a measurement at 40 kN and the solid line represents a measurement with an externally applied force of 60 kN. It is directly apparent from the diagram of FIG. 1 1 that the Vibrational natural frequencies of the individual graphs are shifted. in the

unloaded state, that is at 0 kN, the natural vibration frequency fO is about 85 kHz. At a tensile load of 20 kN, the natural vibration frequency f20 is about 80 kHz. With a mechanical load of 40 kN is the

Natural vibration frequency f40 at about 76 kHz and at a load of 60 kN, the natural vibration frequency f60 is about 71 kHz.

Experiments have shown that the measurements can be repeated any number of times and at different times, and in each case deliver consistent measurement results. Thus, with the measuring system described here, a long-term stable and extremely precise measurement of an axially acting on a connecting element

mechanical force determinable.

The frequency ranges given here are purely exemplary for a prototype. The natural vibration frequency of the at least one sensor element can also be in a completely different frequency range, for example in a range above 100 kHz or even below 10 kHz. Also, depending on the specific design of the connecting element measurement in different power ranges are conceivable. In the flowchart of FIG. 12, the basic method for measuring the force acting on a connector 10 is shown schematically. In a first step 100, a connecting element 10 is provided and its sensor 12 or its sensor element 22, 24 is electrically signal-transmitting connected to a measuring arrangement 30. In a further step 102, the at least one sensor element 22, 24 is acted upon by a time-varying electrical signal, in particular with an input signal generated by the signal generator 32. In a further step 104, which can take place at the same time as step 102, the response signal reflected by the sensor element 22, 24 is measured.

Steps 102 and 104 are typically performed for an entire frequency spectrum. After a frequency spectrum has been analyzed, in a concluding step 106, the natural vibration frequency of the sensor element 22, 24 determined from the measured response signals. The natural vibration frequency can be determined as the frequency at which the amplitude of the response signal for the measured frequency range is maximum. The assignment of the measured natural vibration frequency to a force actually acting on the connecting element then takes place according to a previously performed calibration or calibration.

As further indicated in FIG. 2, the measuring system may also have, in addition to the already described first measuring arrangement 30, a further, namely a second measuring arrangement 130. The signal cable 35 of the sensor 12 can be selectively coupled or connected to either the first or the second measuring arrangement 30, 130. This has the advantage that a

Signal evaluation can be switched without changing the sensor. Thus, e.g. for long-term stable measurements, the first measuring arrangement 30 can be used, while for highly dynamic or particularly sensitive measurements another measuring method according to the second measuring arrangement 130 can be used, e.g. based on a capacitively coupled operational amplifier. One

Switching between the measuring arrangements can be done by means of eg a switch.

Significant l iest

1 component

2 component

3 passage opening

4 passage opening

10 connecting element

11 connecting body

12 sensor

14 cavity

15 sensor section

16 sensor section

17 shaft

18 head

22 sensor element

23 cable feedthrough

24 sensor element

25 external thread

26 electrical contact

27 positive locking structure

28 recording

29 internal thread

30 measuring arrangement

32 signal generators

34 signal receiver

35 signal receiver

36 signal cables

38 resistance

42 nut

45 external thread

46 internal thread

47 positive locking structure measuring system

ground

inner wall

head Start

mounting cap

Cable bushing electrical insulation

Grommet

functional component

connecting body

measuring arrangement

weld

external thread

inner thread

Claims

P a n t a n s p r e c h e

Connecting element (10) with an elongate connecting body (1 1) and with a sensor (12) which in a cavity (14) of the

Connection body (1 1) arranged and fixed to the connecting body (1 1) is connected, wherein the sensor (12) has at least one sensor element (22, 24) with a load-dependent modulus of elasticity, which changes depending on an applied mechanical force and wherein the Sensor element (22, 24) with a measuring arrangement (30) signal-transmitting coupled.

Connecting element (10) according to claim 1, wherein the sensor (12) has a first sensor section (15) and a second sensor section (1 6), which are spaced apart in the longitudinal direction of the connecting body (1 1) and wherein the first sensor section (15). and the second sensor portion (1 6) in each case fixedly connected to the connecting body (1 1) or are fixed thereto.

Connecting element according to one of the preceding claims, wherein the at least one sensor element (22, 24) depending on a

mechanical force variable electrical measurable

Having natural vibration frequency.

Connecting element according to one of the preceding claims, wherein the at least one sensor element (22, 24) comprises a piezoelectric crystal or a piezoelectric ceramic.

Connecting element according to one of the preceding claims, wherein one with the measuring arrangement (30) electrically conductively connectable electrical contact (26) at one longitudinal end of the at least one sensor element (22, 24) is arranged. Connecting element according to one of the preceding claims, wherein the sensor (12) at least two in the longitudinal direction of the connecting body (1 1) spaced sensor elements (22, 24), between which an electrical contact (26) is arranged, which with both sensor elements (22 , 24) is in electrical contact.

A connector as claimed in any one of the preceding claims, wherein the sensor (12) within the cavity (14) is subjected to longitudinal mechanical compression.

Measuring system with at least one connecting element (10) according to one of the preceding claims and with at least one measuring arrangement (30) which can be coupled in signal-transmitting manner with the at least one sensor element (22, 24) of the sensor (12) of the connecting element (10).

Measuring system according to claim 8, wherein the measuring arrangement (30) comprises: at least one electrical signal generator (32) for generating a temporally varying electrical input signal, and at least one first signal receiver (34), wherein the first signal receiver (34) and the signal generator (32 ) are electrically coupled to the at least one sensor element (22, 24) and wherein the first signal receiver (34) for evaluating a response signal of the at least one sensor element (22, 24) is formed.

0. Measuring system according to claim 9, wherein the signal generator (32) and the first signal receiver (34) via a common signal cable (36) with the at least one sensor element (22, 24) are coupled. Measuring system according to claim 9 or 10, wherein the signal generator (32) and the first signal receiver (34) are connected in series via an electrical resistor (38).

Measuring system according to one of the preceding claims, further comprising a second signal receiver (35) which is designed to measure a frequency of the output signal generated by the signal generator (32).

Measuring system according to one of the preceding claims, wherein the first signal receiver (34) for measuring a frequency spectrum of the

Response signal of the at least one sensor element (22, 24) is formed.

Method for measuring a force acting on a connecting element, with the steps:

Providing a connecting element (10) according to one of the preceding claims 1 to 7, electrically connecting the at least one sensor element (22, 24) to a measuring arrangement (30),

Applying the at least one sensor element (22, 24) to a time-varying electrical signal,

Measuring a response signal reflected by the sensor element (22, 24) and

Evaluating the response signal to determine a force acting on the connecting element (10) in the longitudinal direction.

15. The method of claim 14, wherein the evaluating the response signal comprises a spectral analysis of the response signal and wherein for determining the longitudinal force on the connecting element (10) acting force Resonant or natural frequency of the at least one sensor element (22, 24) is measured.