DE102016219953A1 - Method and device for measuring the preload force of a mechanical connection, in particular a screw connection - Google Patents

Abstract

The present invention relates to a method and a device for measuring the prestressing force of a mechanical connection, in particular a screw connection, which is produced between a component and an object or further component via at least one tensioned connection element. In the method, the biasing force is measured with a capacitive pressure sensor, which is integrated in a flat shim with a through hole for the connecting element. The shim is inserted in making the mechanical connection between a head or counterpart of the connecting element and the component. In the method and the device, a capacitive pressure sensor is used, which has at least three pressure-sensitive capacitors around the passage opening, wherein after the production of the mechanical connection adjusting capacitors of the capacitors are detected. With the method and the device, the preload force can be reliably determined and monitored over a longer period of time. The device can be produced inexpensively.

Description

Technical application

The present invention relates to a method for measuring and / or monitoring the biasing force of a mechanical connection, in particular a screw connection, according to the preamble of claim 1. The invention also relates to a trained for performing the method device.

In many technical fields, individual components must be mechanically connected to each other or to, for example, fixed objects. Often this purpose screw connections are used, in which the screw is loaded as a connecting element to train. Especially with safety-relevant connections, it is also necessary to monitor the mechanical connection over time. For example, in the construction of structures adjacent components are often joined together by screws. These must be acted upon with a specified biasing force, which can be achieved by the use of torque wrenches in the manufacture of the screw. However, if the bolt tilts when tightened, the adjusted torque will not match the preload force in the bolt. Furthermore, the screw can loosen over time.

State of the art

So far, the preload force in screw connections in most cases is set only by torque wrench. However, techniques are also known for measuring the preload force during or after making the screw connection via suitable sensors.

That's how it shows DE 10 2012 020 932 A1 a force plate having a plate member and a sensor for detecting forces acting perpendicular to the plate surfaces forces. The sensor is formed by at least one strain sensor which is arranged on a peripheral surface of the plate element. The force measuring plate is designed in one embodiment as an annular washer, which is inserted in the manufacture of the screw connection between the screw head or the nut and the component. Since the washer deforms slightly when the screw connection is made, the tensile force of the screw connection can be detected with the strain sensor.

From the DE 10 2009 043 267 A1 discloses a system for monitoring a screw connection, wherein in one embodiment, a capacitive pressure sensor is used, which is integrated in a washer for the screw connection. About the detection of the capacitance of the capacitive pressure sensor, the biasing force of the screw can then be determined.

However, many of the hitherto available solutions for measuring the preload force of a screw connection do not allow sufficiently cost-effective production in order to be produced and used in large quantities. In addition, the testing of the preload force is often unreliable, since incorrect measurements can occur due to a tilting of the screws.

The object of the present invention is to provide a method and a device for measuring the preload force of a mechanical connection via a loaded on train connecting element, which can be implemented inexpensively and allow reliable detection of the biasing force over a longer period.

Presentation of the invention

The object is achieved by the method and the device according to claims 1 and 9. Advantageous embodiments of the method and the device are the subject of the dependent claims or can be found in the following description and the embodiment.

In the proposed method, the biasing force is measured with a capacitive pressure sensor, which is integrated in a flat shim with a through hole for the connecting element, which is inserted in producing the mechanical connection, in particular a screw, between a head or counterpart of the connecting element and the component , When producing a screw, the screw thus represents the connecting element, wherein the shim is inserted between the screw head and the component or between a nut as a counterpart of the screw and the component. Of course, in this case also one or more washers may additionally be present as intermediate elements. In the method and the proposed device, the passage opening may represent an opening (hole) completely enclosed by the base element, but may be open towards a narrow side of the passage element, ie form a slot open in one side in the base element. In this embodiment, the shim is thus formed as a fork washer having an outer shape similar to a fork cable lug. In this embodiment, it is possible, the shim only after loosely connecting the Insert connecting element with the counterpart (eg screw with nut) laterally over the connecting element. The proposed method is characterized in that for measuring the biasing force, a capacitive pressure sensor is used which has at least three pressure-sensitive capacitors around the passage opening, wherein after the preparation of the mechanical connection adjusting capacity of at least three pressure-sensitive capacitors directly or indirectly, eg ., About the frequency of a resonant circuit formed with these capacitors, are detected.

The proposed method allows by using a capacitive pressure sensor with at least three pressure-sensitive capacitors around the passage opening around a more reliable measurement of the biasing force, since a tilting of the connecting element can be detected immediately. For a uniform connection, for example. Even tightening a screw, the at least three pressure-sensitive capacitors are equally heavily loaded, whereas there is a tilting at different load. By integrating the capacitive pressure sensor in a flat shim that remains between the head or counterpart of the connecting element and the component, the biasing force of the mechanical connection can be measured or monitored over a longer period of time. Thus, it can be determined whether the preload force has decreased immediately after the connection has been established or has decreased over time.

The proposed device for carrying out the method is accordingly designed as a flat shim with a through hole for the connecting element and has the capacitive pressure sensor. The shim may also be composed of several parts. In this case, the capacitive pressure sensor has at least three pressure-sensitive capacitors around the through-opening and electrical connections via which the respective capacitances of the capacitors can be detected.

In a preferred embodiment, the capacitive pressure sensor is formed by a dielectric between two metallic layers, of which at least a first metallic layer is separated into several areas, so that the plurality of pressure-sensitive capacitors, hereinafter also referred to as the two metallic layers with the intermediate dielectric Measuring capacitors referred to are formed around the through hole. Due to the force applied during the production of the mechanical connection, the dielectric of the capacitors is deformed and thus the capacitance of the capacitors is changed. About the electrical connections, the respective capacity or a change in capacity can be detected and evaluated. Thus, the detected capacitance can, for example. With the aid of a calibration curve in the applied force, d. H. the preload force, convert. It is also possible to form a stack of several of these capacitive structures comprising first and second metallic layers with an intermediate dielectric in order to achieve higher capacitances by connecting the measuring capacitors lying one above the other in parallel. The capacitive structures are separated from each other in the stack by an intermediate insulating layer.

In a preferred embodiment, the metallic layers of the capacitive pressure sensor are formed annularly around the passage opening. In this case, the first metallic layer is preferably separated into at least three ring segments, through which the individual measuring capacitors are formed in conjunction with the second metallic layer and the dielectric. When using the stack described above, this separation into ring segments correspondingly affects all the first metallic layers of the respective capacitive structures.

The design of the capacitive pressure sensor with the two metallic layers and the intermediate dielectric allows a very cost-effective production of the proposed device. In this way, the two metallic layers can each be produced on separate carrier plates or boards, between which the dielectric is then introduced during the final assembly of the sensor. The entire shim is preferably formed in the form of a sandwich structure of the two carrier plates or boards with the intermediate dielectric. The non-segmented metallic layer can also be realized by a metallic housing part, in which the board with the segmented metallic layer is inserted. It is also possible to realize the non-segmented metallic layer by a clamping disk or spring washer.

It is also possible to manufacture a single- or multi-layer board in which the carrier material, the dielectric and the copper surfaces and segmented copper surfaces form the capacitor plates. Furthermore, it is possible to apply signal processing electronics to one or both carrier plates or boards or to the single-layer or multilayer board, also referred to below as a sensor board, via which the respective capacitances of the capacitors are detected and provided in an appropriate form at an output terminal. This can be done, for example, by embedding a chip with a microcontroller in the Sensor board done. The microcontroller may also include a temperature sensor that can be used to make an accurate temperature measurement for fine calibration of the pressure sensor as needed. It is also possible to design the transmission of the corresponding measurement signals without contact, for example by using the RFID technology. For this purpose, a corresponding RFID unit is then applied or integrated on one or both carrier plates or boards or on the single or multilayer board. Alternatively, the above microcontroller may also have an RFID function. Automatic capacitor switching, phantom power, or other techniques for operating the pressure sensor may also be implemented to minimize the number of connection lines to the pressure sensor.

The signal processing electronics are preferably designed such that they convert the detected capacitances in each case into a frequency. This eliminates advantageous capacitive influences for further signal processing.

In an advantageous embodiment of the proposed method and the associated device, the shim is formed so that it also has an unloaded from the mechanical connection area that is not affected by the biasing force of the mechanical connection. In this unloaded region, a further capacitor is arranged as a reference capacitor, whose capacitance is also detected in this embodiment. Capacitance changes can be compensated for by forming the ratio of the respectively measured capacitances of the capacitors in the loaded area, hereinafter also referred to as measuring capacitors, or the quantities, in particular frequencies, measured to detect the capacitances and the capacitance of the reference capacitor in the unloaded area or the corresponding measured variable that are not caused by the mechanical connection. This concerns in particular the compensation of temperature effects. Preferably, the unloaded area is additionally decoupled mechanically from the loaded area by means of a suitable partially circumferential slot in the shim or at least one of the shims of the shim (using the above sandwich structure). The slot encloses the unloaded area with the reference capacitor by at least 180 °.

The proposed method and the proposed device can be used particularly advantageously for checking and / or monitoring the prestressing force in the production of screwed connections. However, it is also possible to use the method and apparatus for other types of mechanical connections that are made via a tensioned connector. An example of this are rivet or pin connections.

list of figures

• 1 eine schematische Darstellung einer als Unterlegscheibe ausgebildeten Vorrichtung gemäß der vorliegenden Erfindung;
• 2 ein Beispiel für die Ausgestaltung der beiden Metallisierungsschichten auf zwei Platinen, aus denen die vorgeschlagene Vorrichtung zusammengesetzt wird;
• 3 ein Beispiel für eine Seite einer der beiden Platinen der 2, auf der die elektronische Schaltung zur Signalverarbeitung sowie die elektrischen Anschlüsse integriert sind;
• 4 ein Beispiel für eine elektronische Schaltung zur Umsetzung der Kapazitäten in Frequenzen; und
• 5 ein Beispiel für eine Realisierung des vorgeschlagenen Unterlegscheibensensors mit Gehäuse.

The proposed method and the associated device will be explained in more detail using an exemplary embodiment in conjunction with the drawings. Hereby show:

• 1 a schematic representation of a washer designed as a device according to the present invention;
• 2 an example of the design of the two metallization layers on two boards, from which the proposed device is assembled;
• 3 an example of one side of one of the two boards of the 2 on which the electronic circuit for signal processing and the electrical connections are integrated;
• 4 an example of an electronic circuit for the conversion of the capacities in frequencies; and
• 5 an example of an implementation of the proposed Unterlegscheensensors with housing.

Ways to carry out the invention

The proposed device will be explained in more detail using an exemplary embodiment in conjunction with the drawings. 1 shows a schematic representation of an example of the embodiment of the device in the form of a washer sensor, which is inserted in the proposed method, for example. Between the screw head and the component to be connected. In the upper part of this illustration is a plan view of this washer sensor 1 represented, which has a corresponding passage opening 2 has, through which the screw is guided. Around this passage opening 2 around the pressure-sensitive measuring capacitors are formed, which are not visible in this illustration. The same applies to the signal processing electronics and the reference capacitor, which in the bottom of the figure in the washer sensor 1 are integrated. The washer sensor in the present example consists of two superimposed boards, between which a film or layer of a dielectric is embedded. This sandwich construction is schematically in the cross-sectional view of the lower part of the figure 1 to recognize the first board 3 , the dielectric 4 as well as the second board 5 shows.

When using this washer sensor when tightening the screw, a compressive force corresponding to the biasing force of the screw on the dielectric 4 exercised. This force causes a change in the geometric strength of the dielectric 4 and thus the distance between the respective metallizations or metallization layers, between which the dielectric 4 located. The metallizations are located on the two boards 3 . 5 and each form with the intervening dielectric 4 the measuring capacitors. The applied force becomes the dielectric 4 deformed and thus changed the capacity of each measuring capacitor. This capacity or capacitance change is measured and can be converted, for example, with the aid of a calibration curve into the applied force. The washer sensor also allows a permanent monitoring of the respective biasing force.

To determine a tilting of the screw at least one of the metallizations is divided into several areas or segments, whereby a plurality of measuring capacitors are formed. With uniform tightening the respective segments or capacitors are charged equally, whereas at different load there is a tilting.

2 shows an example of the design of the metallizations of the first board 3 as well as the second board 5 , The figure shows this in each case to the dielectric 4 directed sides of these boards. The first metallization 6 the first board 3 is divided into three segments. The second metallization 7 the second board 5 is, however, as a closed ring around the passage opening 2 educated. When assembling the two boards 3 . 5 with an intermediate dielectric 4 thereby become three measuring capacitors around the passage opening 2 formed around, whose capacity is measured by a signal processing electronics, not shown in this figure. In the lower part of the two boards 3 . 5 each is another metallization 8th to detect, by which a reference capacitor for the measurement is formed. This reference capacitor is located in an area not stressed by the screw connection to be measured. This is in addition to the second board 5 a partially rotating slot 9 introduced the dielectric 4 In this area additionally decoupled from the mechanical load through the screw.

1. 1. Kupferfläche (Schirm),
2. 2. Platinenmaterial,
3. 3. segmentierte Kupferflächen (erste metallische Schicht bzw. Platte der Messkondensatoren),
4. 4. Dielektrikum verformbar,
5. 5. Kupferfläche (zweite gemeinsame metallische Schicht bzw. Platte der Messkondensatoren),
6. 6. Platinenmaterial,
7. 7. Kupferfläche (Schirm, kann entfallen).

Die Kupferflächen sind alle mit der GND (Masse) verbunden, die segmentierten Flächen sind Signalführend. Die beiden äußeren Kupferflächen dienen bei diesem Beispiel lediglich als Abschirmung gegen Störeinflüsse.The capacitive pressure sensor can also have further layers, for example for shielding against interference. For example, the capacitive pressure sensor could have the following stratification:

1. 1. copper surface (screen),
2. 2. board material,
3. 3. Segmented copper surfaces (first metallic layer or plate of the measuring capacitors),
4. 4. Dielectric deformable,
5. 5. Copper surface (second common metallic layer or plate of the measuring capacitors),
6. 6. board material,
7. 7. Copper surface (screen, can be omitted).

The copper surfaces are all connected to the GND (ground), the segmented surfaces are signal leading. The two outer copper surfaces serve in this example only as a shield against interference.

1. 1. Kupferfläche (Schirm),
2. 2. Platinenmaterial,
3. 3. segmentierte Kupferflächen (erste metallische Schicht bzw. Platte der Messkondensatoren, 1. Schicht),
4. 4. Dielektrikum verformbar,
5. 5. Kupferfläche (zweite gemeinsame metallische Schicht bzw. Platte der Messkondensatoren, 1. Schicht),
6. 6. Platinenmaterial,
7. 7. segmentierte Kupferfläche, (erste metallische Schicht bzw. Platte der Messkondensatoren, 2. Schicht),
8. 8. Dielektrikum verformbar,
9. 9. Kupferfläche (zweite gemeinsame metallische Schicht bzw. Platte der Messkondensatoren, 2. Schicht),
10. 10. Platinenmaterial,
11. 11. Kupferfläche (Schirm, kann entfallen).

Die Kupferflächen sind wieder alle mit GND (Masse) verbunden. Die jeweils übereinanderliegenden Kupfersegmente werden miteinander verbunden (Parallelschaltung der Kondensatoren). Dadurch ergibt sich für die vier Kondensatoren eine doppelte Kapazität.It is also possible to stack a plurality of such capacitive structures of first and second metallic layer with interposed dielectric in order to achieve higher capacitances. In this stacking, however, the pressure sensor should no longer be assembled from individual parts but formed integrally, wherein electrical connections between the layers in the unloaded part of the sensor are generated via vias. An example of a double layering according to this system:

1. 1. copper surface (screen),
2. 2. board material,
3. 3. segmented copper surfaces (first metallic layer or plate of the measuring capacitors, 1st layer),
4. 4. Dielectric deformable,
5. 5. Copper surface (second common metallic layer or plate of the measuring capacitors, 1st layer),
6. 6. board material,
7. 7. segmented copper surface, (first metallic layer or plate of the measuring capacitors, 2nd layer),
8. 8. Dielectric deformable,
9. 9. Copper surface (second common metallic layer or plate of the measuring capacitors, 2nd layer),
10. 10. board material,
11. 11. Copper surface (screen, can be omitted).

The copper surfaces are again all connected to GND (ground). The superimposed copper segments are connected to each other (parallel connection of the capacitors). This results in a double capacity for the four capacitors.

In the example of 1 and 2 The capacitance of the respective capacitors via a signal processing electronics 10 converted into a frequency to exclude capacitive influences for further signal processing. This signal processing electronics 10 is in this example in the first board 3 integrated, like this in 3 is indicated schematically. 3 shows a plan view of the dielectric 4 opposite side of the first board 3 , The field of integrated signal processing electronics 10 is indicated here only schematically. Furthermore, in this illustration electrical connection surfaces 11 for the power supply, the output signal of the signal processing electronics 10 as well as to detect the activation of the sensor.

The measurement or signal processing of the capacitances of the individual capacitors takes place in this example with the aid of a multiplexer with which the capacitances of the capacitors are detected in chronological order. 4 shows an example of such a signal processing electronics 10 , This signal processing electronics has in the present example a voltage regulator 13 to power the individual components, via a power supply input 12 is fed. The capacitances of the measuring capacitors CS1, CS2 and CS3 and of the reference capacitor CR1 are transmitted via the analog multiplexer 14 measured consecutively. The analog multiplexer 14 In turn, it is controlled by external binary switches, which are controlled via corresponding control inputs 15 be connected to the signal processing electronics. The respective measured capacitances are via a Schmitt trigger 16 converted into frequencies that are at the frequency output 17 be provided to the signal processing electronics of the washer sensor. In the diagram of the 4 represent C1 to C6 capacitances, R1 to R5 resistors and L an inductive filter element. The respective output signal corresponds to a frequency which decreases with increasing pressure on the dielectric. From the frequency, the corresponding preload force can be determined via a calibration curve.

The washer sensor described in this example can be realized, for example, with a thickness of only about 1 mm and well below. Depending on the dielectric used and the area of the metallizations, the capacitance for the reference capacitor and the measuring capacitors in the unloaded state can be, for example, in the range between 10 and 100 pF.

5 shows in plan view and in cross section an example of an implementation of the proposed washer sensor, in which the sensor board 18 surrounded by the reference and the measuring capacitors of a protective housing. This housing is characterized by an upper housing part 19 and a lower housing part 20 formed between which the sensor board 18 is inserted with the integrated, deformable dielectric. The housing parts are designed as specially shaped washers and with a rotation 21 secured against twisting when tightening. In the present example, the upper housing part 19 as anti-twist device 21 the two recognizable in the figure noses, which in corresponding receptacles on the lower housing part 20 intervention.

LIST OF REFERENCE NUMBERS

1

Unterlegscheibensensor

2

Through opening

3

first board

4

dielectric

5

second board

6

first metallization

7

second metallization

8th

Metallization for reference capacitor

9

slot

10

Signal processing electronics

11

electrical connection surfaces

12

Power Input

13

voltage regulators

14

analog multiplexer

15

Control inputs for external binary switches

16

Schmitt trigger

17

frequency output

18

sensor board

19

Upper housing part

20

Lower housing part

21

twist

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012020932 A1 [0004]
• DE 102009043267 A1 [0005]

Claims (17)

Method for measuring and / or monitoring the pretensioning force of a mechanical connection, in particular a screw connection, which is produced between a component and an object or further component via at least one tensioned connection element, in which the pretensioning force is measured with a capacitive pressure sensor which is in a flat shim (1) with a through hole (2) is integrated for the connecting element, wherein the flat shim (1) is inserted in establishing the mechanical connection between a head or counterpart of the connecting element and the component, characterized in that a capacitive pressure sensor is used, which has at least three pressure-sensitive capacitors (CS1, CS2, CS3) around the passage opening (2) around, which adjusts after the preparation of the mechanical connection adjusting capacitors of the capacitors (CS1, CS2, CS3) for measuring the biasing force. Method according to Claim 1 characterized in that the capacitive pressure sensor comprises a capacitive structure of a dielectric (4) between two metallic layers (6, 7) which deforms by making the mechanical connection, at least a first (6) of the metallic layers forming multiple regions separated by the two metallic layers (6, 7) with the intermediate dielectric (4) to form the plurality of pressure-sensitive capacitors (CS1, CS2, CS3) around the passage opening (2) around. Method according to Claim 2 , characterized in that the capacitive pressure sensor comprises a stack of a plurality of the capacitive structures, in which in each case superimposed pressure-sensitive capacitors are connected in parallel. Method according to one of Claims 1 to 3 , characterized in that also the capacitance of a reference capacitor (CR1) is detected, which is arranged in a not loaded by the mechanical connection region of the shim (1). Method according to one of Claims 1 to 4 , characterized in that the capacitances of the capacitors (CS1, CS2, CS3, CR1) are converted into frequencies via an electrical circuit (10). Method according to one of Claims 1 to 5 , characterized in that the biasing force is determined via a calibration curve from the detected capacitances or variables derived therefrom. Method according to one of Claims 1 to 6 , characterized in that the biasing force is measured continuously or repeatedly after production of the mechanical connection. Method according to one of Claims 1 to 7 , characterized in that it is checked by comparing the capacitances of the plurality of capacitors (CS1, CS2, CS3) or variables derived therefrom, whether a tilting of the connecting element is present. Device for measuring and / or monitoring the prestressing force of a mechanical connection, in particular a screw connection, which is produced between a component and an object or further component via at least one tensioned connection element, wherein the device is designed as a flat lower element (1) with a passage opening (1). 2) is designed for the connecting element and has a capacitive pressure sensor, characterized in that the capacitive pressure sensor has at least three pressure-sensitive capacitors (CS1, CS2, CS3) around the passage opening (2) and electrical connections over the capacitances of the capacitors (CS1 , CS2, CS3) can be detected. Device after Claim 9 , characterized in that the capacitive pressure sensor comprises a capacitive structure of a dielectric (4) between two metallic layers (6, 7), of which at least one first (6) is separated into a plurality of areas to pass through the two metallic layers (6 , 7) with the intermediate dielectric (4) to form the plurality of pressure-sensitive capacitors (CS1, CS2, CS3) around the passage opening (2). Device after Claim 10 , characterized in that the capacitive pressure sensor comprises a stack of a plurality of the capacitive structures, in which in each case superimposed pressure-sensitive capacitors are connected in parallel. Device after Claim 10 or 11 , characterized in that the metallic layers (6, 7) are formed annularly around the passage opening (2). Device after Claim 12 , characterized in that the first metallic layer (6) is separated into at least three ring segments. Device according to one of Claims 10 to 13 , characterized in that the shim (1) in sandwich construction of two support plates (3, 5) with the intermediate dielectric (4) is formed, wherein the two metallic Layers (6, 7) on the two support plates (3, 5) are formed. Device according to one of Claims 10 to 13 , characterized in that the shim (1) is made of a single- or multilayer board, which has a carrier material and copper surfaces, wherein the carrier material, the dielectric (4) and the copper surfaces, the metallic layers (6, 7) for the capacitors (CS1 Form, CS2, CS3). Device according to one of Claims 9 to 15 , characterized in that the shim (1) has a load-free area, which is not loaded by the mechanical connection when inserting the shim (1) between a head or counterpart of the connecting element and the component, wherein in the unloaded area, a reference capacitor (CR1 ) is arranged for the measurement. Device according to one of Claims 9 to 16 , characterized in that an electrical circuit (10) for detecting the capacitances of the capacitors (CS1, CS2, CS3, CR1) arranged on the shim (1) or in the shim (1) is integrated.

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