Device and method for monitoring a screw connection

Abstract

The invention relates to a device for monitoring at least one screwed joint (3) for breakage. The device has at least one electrically conductive contact element (11) arranged in the direction of an axial extension of the screw, which is spaced apart from the screwed joint when it is intact and is electrically insulated from it. The device further has a measuring device (16) configured to detect electrical contact between the screwed joint (3) and the at least one contact element (11). The invention further relates to a method for monitoring at least one screwed joint (3) for breakage.

Description

[0001] The invention relates to a device for monitoring at least one screw connection comprising a screw for breakage. The invention further relates to a method for monitoring such a screw connection.

[0002] Highly stressed bolted connections, such as those in wind turbines, are monitored for safety reasons to detect any damage as quickly as possible. Such highly stressed bolted connections are used in wind turbines, for example, to fasten flanges, with a large number of bolted connections arranged around the circumference of the flange. Flanges are used in wind turbines, for example, to connect tower segments, to attach slewing rings for a nacelle to the tower or nacelle, and to mount rotor blades to a rotor hub.

[0003] By monitoring a screw connection break, personal injury and / or economic consequential damage that can occur if a screw break goes undetected can be avoided.

[0004] For monitoring screw connections, a monitoring attachment is known from document EP 3047144B1, for example, which radially surrounds the circumference of a screw nut. If damaged, for example, if the nut bursts, the attached monitoring attachment is also destroyed. The monitoring body has a circumferential electrical conductor that is interrupted if the attachment is damaged, which is detected.

[0005] In a further development, a similar arrangement is known from WO 2022 / 063978 A1, in which the monitoring attachment is not destroyed, but is formed in two parts, with the two parts joined by a plug connection. If the nut bursts, the plug connection is opened, which also allows the detection of a destruction of the nut. The monitoring attachment itself is advantageously reusable.

[0006] The monitoring attachments described have proven their worth in practice for monitoring nuts in a bolted connection. However, they are not capable of detecting a broken bolt in a bolted connection if the part of the bolted connection on which the monitoring attachment is mounted is not damaged and remains in place.

[0007] It is an object of the present invention to describe a monitoring device for a screw connection that can, in particular, detect the breakage of a screw of the screw connection. A further object is to provide a method for detecting the breakage of a screw connection in such a device.

[0008] This object is achieved by a device and a method having the features of the respective independent claim. Advantageous embodiments and further developments are the subject of the dependent claims.

[0009] A device according to the invention for monitoring at least one screw connection comprising a screw for breakage has at least one electrically conductive contact element arranged in the direction of an axial extension of the screw and, when the screw connection is intact, spaced from it and electrically insulated from it. Furthermore, a measuring device is provided which is configured to detect electrical contact between the screw connection and the at least one contact element. A screw of a monitored screw connection can have either a screw head or be designed as a so-called screw bolt onto which a nut is screwed.

[0010] If a screw connection breaks, for example, if the screw breaks, the broken part of the screw, including the screw head or a screwed-on nut, moves axially out of the bore in which the screw is located. The broken part of the screw hits the contact element, causing the screw and the contact element to make electrical contact. This is then detected by the measuring device, which subsequently emits an alarm signal.

[0011] To detect contact, the measuring device is connected, for example, directly to at least one contact element and usually indirectly to the screw connection. If the screw connection is located in a bore of a flange, for example, the measuring device can be electrically connected to the flange, thereby establishing electrical contact with the contact element via the flange and the broken-off part of the screw.

[0012] The alarm signal is preferably provided as an electrical signal or as a digital alarm message that can be transmitted via a data transmission channel. Another advantage of the device is that the contact element mechanically prevents the remaining screw from falling out of the hole, thus preventing people from being injured or material from being damaged by falling parts.

[0013] A method according to the invention for monitoring at least one screw connection having a screw for breakage comprises the following steps: At least one electrically conductive contact element is arranged in the direction of an axial extension of the screw, wherein the at least one electrically conductive contact element has no electrical contact with the at least one screw connection when the screw connection is intact. It is then detected whether there is electrical contact between the at least one screw connection and the at least one contact element. An alarm signal is emitted if electrical contact is detected between the at least one screw connection and the at least one contact element.

[0014] To detect contact, the at least one electrically conductive contact element is preferably connected, on the one hand, to a high-impedance voltage or current source and, on the other hand, to at least one measuring input of the measuring device. The measuring input can then be monitored for a potential change that occurs when the torn-off part of the screw connection contacts the contact element. For this purpose, the contact element can, for example, be brought by the high-impedance voltage or current source to a potential that differs from a (ground) potential of the flange. Contact between the contact element and the flange via the torn-off part of the screw connection then leads to a potential change at the measuring input.

[0015] For use of the device for monitoring screw connections of a flange, the at least one electrically conductive contact element is advantageously a circular or circular arc-shaped sheet metal which particularly effectively covers a plurality of screw connections of the flange.

[0016] In an advantageous embodiment of the device, the at least one electrically conductive contact element is connected to electrically insulating spacers, which hold it in the correct position in front of the screw connections. When monitoring screw connections of a flange, the electrically insulating spacers are arranged, for example, on the upper side of the flange.

[0017] In a further advantageous embodiment, the device has at least two electrically conductive contact elements and the measuring device has at least two measuring inputs, each of which is connected to one of the electrically conductive contact elements. In a further development of the method, it can then be provided to compare the at least two measuring inputs with one another and to ignore voltage jumps that are observed synchronously at both measuring inputs. Since it is very unlikely that two screw connections in the area of ​​the at least two contact elements will loosen simultaneously and lead to the same time curve of the voltages at the two measuring inputs, voltage jumps observed synchronously at both measuring inputs can be attributed with a very high probability to electromagnetic interference, e.g. lightning. Through this type of evaluation, the probability of errors when issuing an alarm signal can be reduced.

[0018] The invention is explained in more detail below using an exemplary embodiment and the accompanying figures. The figures show: Fig. 1 shows an overall view of a flange with a plurality of screw connections and electromechanical components of a device for monitoring the screw connections; and Fig. 2 a section of the flange according to Fig. 1 in an oblique view together with a schematic representation of further components of the device for monitoring the screw connections.

[0019] In both figures, identical reference symbols identify identical or identically functioning elements. For reasons of clarity, not every element in each figure is provided with a reference symbol.

[0020] Fig. Figure 1 initially shows an isolated flange 1 of a flange connection. The flange 1 shown has two concentrically arranged hole rings 2, each of which can accommodate a plurality of screws, bolts, or threaded rods.

[0021] Purely as an example, screw connections 3 are only in the outer of the hole rings 2 in the Fig. 1. Each hole in this outer hole ring 2 accommodates a screw of one of the screw connections 3.

[0022] The flange 1 is provided with two contact elements 11, which in this exemplary embodiment essentially have the shape of a half-circular ring, the diameter of which corresponds to the diameter of the outer perforated ring 2. The two contact elements 11 are arranged with a plurality of spacers 12 in the axial extension of the screw connections 3. The respective contact element 11 can be formed in one piece or consist of a number of sub-segments that are mechanically and electrically connected to one another. The contact elements 11 are made of a conductive material, preferably a corrosion-free metal such as stainless steel. In addition to the spacers 12, two connections 13 are arranged laterally on the flange 1 for each contact element 11, each located on an electrically insulating connection base 14.The spacers 12 are also electrically insulating, so that the contact element 11 can be brought to a potential via the connections 13 that is different from a potential of the flange 1 and thus of the screw connections 3.

[0023] Fig. 2 shows a section of the flange 1 according to Fig. 1 in a three-dimensional oblique view. Also shown is a measuring device 16, which is connected to the contact elements 11 and the flange 1 and serves to detect a break in one of the screw connections 3. Together with the contact element 11, the measuring device 16 forms a device for detecting a break in one of the screw connections 3.

[0024] In Fig. 2 it can be seen that in this embodiment 2 the screw connections 3 are each made with screws, of which in the Fig. 2, a screw head 4 can be seen in each case. The screws are inserted into the bores of the outer hole ring 2 of the flange 1 with additional washers 5 underneath and screwed there. A nut can be screwed onto each of the screws on the opposite side of the flange 1, not visible here. As already mentioned at the beginning, a screw connection 3 monitored according to the invention can be designed not only with a screw with a screw head 4, as shown here as an example, but also with screws without a screw head, which are also referred to as screw bolts and onto which a nut is screwed.

[0025] In the oblique view of the Fig. 2 shows that an air gap remains between the axially outer surface of the screw head 4 and the underside of the contact element 11. With correct screw connections 3, there is therefore no mechanical or electrical contact between one of the screw heads 4 and one of the contact elements 11.

[0026] If one of the screw connections 3 breaks, the Fig. 2 The upper, broken-off part of the screw, including the screw head 4, is no longer firmly seated in the bore of the flange 1. Without the contact elements 11, there would be a risk of this screw remnant falling out of the bore of the flange 1 and injuring people or damaging material. Due to the upstream contact element 11, the screw remnant of the damaged screw connection 3 is advantageously prevented from falling out in a purely mechanical manner.

[0027] When the screw head 4 of the broken screw connection 3 rests against the contact element 11, this contact element 11 is electrically connected to the flange 1 via the broken screw.

[0028] In a method according to the invention, such an electrical connection between the flange 1 and the at least one contact element 11 is detected. Upon detection of contact, a corresponding alarm signal is issued.

[0029] In the lower part of the Fig. 2 shows the measuring device 16 together with further electrical and electronic components for carrying out such a method.

[0030] The terminals 13 of the two contact elements 11 and also the flange 1 are connected to the measuring device 16 via connecting cables 15. The flange 1 is connected to a ground potential GND via the measuring device 16. The terminals 13 are connected to the measuring inputs 17 of the measuring device 16 and are additionally supplied with a voltage potential +Vc that is positive relative to the ground potential GND via resistors 18, which are connected here as so-called pull-up resistors. The potential present at the measuring inputs 17 is measured continuously or at regular intervals.

[0031] If all screw connections 3 are intact and there is no electrical contact between the flange 1 and one of the contact elements 11, both connections 13 are at the positive voltage potential +Vc. If contact is made between the flange 1 and the contact element 11 through a broken screw connection 3, the corresponding contact element 11 and thus the corresponding connection 13 or the corresponding measuring input 17 are pulled down to the ground potential GND, which is detected by the measuring device 16.

[0032] Since, especially in the case of a rotating flange 1, no permanent low-resistance connection will generally form between the flange 1 and the contact element 11, a potential that jumps back and forth between the positive voltage potential +Vc and the ground potential GND will typically be measured at the measuring input 18.

[0033] It can be provided that even a single, brief detection of the ground potential GND at one of the measuring inputs 17 by the measuring device 16 triggers an alarm signal to signal a break in one of the screw connections 3. Alternatively, it can also be provided that a single, brief detection of the ground potential GND at one of the measuring inputs 17 is ignored by the measuring device 16, as it could also be due to an interference caused by electromagnetic interference, for example, a lightning strike. To avoid false signaling, the signal at the measuring input 17 can be filtered so that a signal is only generated when the ground potential GND is detected over a longer period of time or when the ground potential GND is detected repeatedly within a certain period of time.

[0034] Furthermore, it can be provided to compare the two measuring inputs 17 with each other and to ignore voltage jumps that are observed synchronously at both measuring inputs 17. Since it is very unlikely that two screw connections 3 in the area of ​​both contact elements 11 will loosen simultaneously and lead to the same time profile of the voltages at the two measuring inputs 17, voltage jumps observed synchronously at both measuring inputs 17 can be attributed with a very high probability to atmospheric electromagnetic interference. Such an evaluation can reduce the probability of errors when issuing an alarm signal.

[0035] The measuring device 16 is preferably arranged in the immediate vicinity of the flange 1 and moves with it. In the illustrated embodiment, the measuring device 16 is connected to a gateway 20, in particular an IoT (Internet of Things) gateway, via a data connection 19. The data connection 19 can be a data bus, for example a CAN bus. The gateway 20 sends the data in the received or processed form via further data connections and a network 21, e.g. the Internet, to a monitoring device 22, which can then be viewed by a user in a monitoring station outside the wind turbine and which displays the alarm messages issued by the measuring device 16 regarding a break in one of the screw connections 3. Reference symbol 1 flange 2 hole ring 3 screw connection 4 screw head 5 Washer 11 Contact element 12 spacers 13 Connection 14 connection sockets 15 connection cables 16 Measuring device 17 Measuring input 18 pull-up resistor 19 Data connection 20 Gateway 21 Network 22 Monitor setup QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This 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

[0000] EP 3047144B1

[0004] WO 2022 / 063978

[0005]

Claims

[1] Device for monitoring at least one screw connection (3) having a screw for a break, comprising - at least one electrically conductive contact element (11) which is arranged in the direction of an axial extension of the screw, which is spaced from the screw when the screw connection is intact and is electrically insulated from it, and - a measuring device (16) which is designed to detect an electrical contact between the screw connection (3) and the at least one contact element (11). [2] Device according to claim 1, wherein the at least one electrically conductive contact element (11) is a circular or circular arc-shaped sheet metal. [3] Device according to claim 2, wherein the at least one electrically conductive contact element (11) covers a plurality of screw connections (3) of a flange (1). [4] Device according to one of claims 1 to 3, wherein the at least one electrically conductive contact element (11) is connected to electrically insulating spacers (12). [5] Device according to claim 3 and 4, wherein the electrically insulating spacers (12) are arranged on an upper side of the flange (1). [6] Device according to one of claims 1 to 5, wherein the at least one electrically conductive contact element (11) is connected to a high-impedance voltage or current source and to at least one measuring input (17) of the measuring device (16). [7] Device according to claim 6, comprising a plurality of electrically conductive contact elements (11), wherein the measuring device (16) has a plurality of measuring inputs (17) which are each connected to one of the electrically conductive contact elements (11). [8] Method for monitoring at least one screw connection (3) having a screw for a break, comprising the following steps: - arranging at least one electrically conductive contact element (11) in the direction of an axial extension of the screw, wherein the at least one electrically conductive contact element (11) has no electrical contact with the at least one screw connection (3) when the screw connection (3) is intact; - detecting whether there is an electrical contact between the at least one screw connection (3) and the at least one contact element (11); and - Emitting a warning signal when an electrical contact is detected between the at least one screw connection (3) and the at least one contact element (11). [9] Method according to claim 8, wherein in the step of detecting, the at least one electrically conductive contact element (11) and the screw connection are subjected to a high-resistance voltage source with different electrical potentials and a change in the potential of the at least one electrically conductive contact element (11) is detected. [10] Method according to claim 9, in which at least two electrically conductive contact elements (11) are assigned to different screw connections (3), wherein the warning signal is only output if a potential change is not detected simultaneously for the at least two contact elements (11).

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