Washer for measuring force and distributing force when connecting a connection means to a part to be connected

Abstract

The invention relates to a washer for measuring force and distributing force when connecting a connection means to a part to be connected, wherein the washer comprises a housing having an upper part and a lower part, and a cavity inside the housing, and a force sensor element is arranged in the hollow chamber and the force sensor element comprises at least one electrode and one dielectric, wherein at least one recess is arranged adjacent to the cavity in the housing so that, when an eccentric force is introduced when the connection means is connected to the part to be connected, the washer can be reproducibly deformed and the introduced force can be reproducibly measured by means of the force sensor element.

Description

Washer for force measurement and force distribution when connecting a fastener to a part to be connected

[0001] The invention relates to a washer for measuring and distributing force when connecting a connecting means to a part to be connected, wherein the washer has a housing with an upper part and a lower part and a cavity inside the housing, and a force sensor element is arranged in the cavity and the force sensor element has an electrode and a dielectric.

[0002] A washer is typically placed over the shank of a screw and serves to transfer the force exerted on the underside of the screw head, when installed, to a larger surface area of ​​the part being connected with the screw. The safety requirements for screw connections are particularly stringent for safety-critical screw connections (Category A). This is the case, for example, with wind turbines, where a reduction in force or complete failure of the screw connection can lead to considerable consequential costs. Unplanned maintenance work on offshore wind turbines, in particular, represents a high cost risk and involves a great deal of effort.

[0003] During assembly, various tightening methods, such as angle-controlled, Yield-point controlled, hydraulic, thermal, torque-controlled and / or pulse-controlled tightening methods, the preload generated in a screw is indirectly measured to ensure that the required preload is applied on the one hand and that the screw connection is not overloaded on the other. However, this does not allow any undershoot of the required preload or even a failure of the screw connection to be detected during operation. A loss of preload during operation can occur, for example, through settling in the contact and bearing surfaces due to leveling of surface irregularities and / or thread flanks. In addition to the time-consuming manual screw check, it is known to arrange force measuring rings in the screw connection or strain gauges on a screw or to carry out an ultrasonic length measurement of the screw.The disadvantage here is that this measuring technology has to be installed in addition to the actual screw assembly and increases the installation space. A force measuring ring is usually two to three times higher than a standard washer. The diameter of the force measuring ring is also usually larger than the diameter of the corresponding standard washer because a correspondingly large cavity has to be provided to accommodate a measuring sensor according to the state of the art. By introducing a separate measuring body such as a force measuring ring, at least the clamped length of the clamping package is increased. This means that the original and tested screw combination can no longer be used. In addition. By incorporating a separate measuring body into the bolted joint, the number of joints is reduced, thus changing the setting behavior of the bolted joint. Furthermore, by incorporating a state-of-the-art measuring body, the rigidity of the clamping assembly is significantly reduced.

[0004] DE 10 2011 005 371 A1 discloses a device for monitoring the integrity of a screw connection, wherein a casing is designed as a locking washer and has a pressure sensor for recording pressure from components of a screw connection when the pressure sensor is arranged between the components of the screw connection and the screw connection is tightened, a computing unit for determining safety information from pressure information of the pressure sensor and a radio interface for transmitting the safety information to an external reading device.

[0005] In WO 2019 / 154827 A1, a washer unit for use on a screw is disclosed, wherein the washer unit comprises a washer and a strain detection element, and the strain detection element is arranged within a passage within a body of the washer, and at least one end of the passage opens to an edge of the body of the washer, and the strain detection element is configured to detect a strain in the direction of the passage. The strain detection element has a length and a width of at least 1 mm to 10 mm each and a height of at least 0.01 mm to a maximum of 1.0 mm. The disadvantage here is that the stiffness of the washer body is reduced by the passageway in which the strain detection element is accommodated. Furthermore, the strain can only be detected in the direction of the passageway. Since at least one passageway runs centrally over the height of the washer body, an off-center force introduction cannot be detected with this washer unit.

[0006] From DE 41 42 141 A1 a device for measuring forces is known which can be designed in the form of a washer and has a force-reducing means which is assigned to a measuring sensor and ensures that the measuring sensor is only subjected to a part of the total force acting on the measuring device. The force-reducing means designed as a force introduction element surrounds a solid base body in the form of a cylindrical ring, wherein the underside of the force introduction element rests on the measuring sensor and the measuring sensor is in turn arranged on a carrier plate which has at least one section projecting beyond an outer circumference of the force introduction means, on which section reference resistors for the measuring resistors of the measuring sensor are arranged. Thus, this measuring device does not have the shape and dimensions of a standard washer. In addition, the force-reducing agents specifically achieve a lower spring stiffness than the base body.

[0007] DE 10 2019 103 625 A1 claims a force measuring device for measuring and monitoring a preload force of a mechanical connection, wherein the force measuring device has two disc-shaped force-absorbing bodies with a central through-opening for the passage of a threaded rod along a force measuring device longitudinal axis, wherein a plurality of sensor elements are arranged between the two disc-shaped force-absorbing bodies, which are each spaced radially from the force measuring device longitudinal axis and an elastically deformable load element is arranged between the first and second disc-shaped force-absorbing bodies for transmitting the preload applied by the threaded rod from the first to the second force-absorbing body, wherein the sensor elements are arranged in an outer load-free area which does not transmit any preload force between the two disc-shaped force-absorbing bodies,to prevent damage to the sensor elements.

[0008] DE 10 2016 219 953 A1 describes a device for measuring and / or monitoring the pre-tensioning force of a mechanical connection, which is designed as a flat support element with a through-opening for the connecting element and has a capacitive pressure sensor, wherein the capacitive pressure sensor has at least three pressure-sensitive capacitors around the through-opening and electrical connections, via which capacitances of the capacitor can be detected. The pressure sensor has a first circuit board and a second circuit board, between which a dielectric is arranged, wherein when a screw is tightened a compressive force corresponding to the preload force of the screw is exerted on the dielectric of the pressure sensor, whereby the distances between the metallizations on the two circuit boards change, which, together with the dielectric in between, form a measuring capacitor. A reference capacitor is arranged in an area of ​​the support element which is not loaded by the screw connection to be measured, whereby one of the circuit boards projects beyond a disc shape and is extended.

[0009] DE 198 31 372 A1 discloses a device for monitoring frictional connections with at least one washer-shaped component in which an inner disk is integrated. The inner disk is formed externally with a high-strength insulating coating, with the exception of one ring, while a measuring layer is arranged on the underside of the inner disk, surrounded by the component.

[0010] DE 11 24 729 A discloses a device for measuring the forces between components within an assembly with a washer, which consists of two partial discs and a piezoelectric crystal arrangement arranged between them. Two sleeves are arranged on the outer and inner circumference, which act as a tube spring in order to press the two partial discs against the crystal arrangement arranged between them with a preload. In an alternative, recesses are arranged opposite one another on a circumferential surface of the upper partial disc, into which sleeve-like projections of the lower partial disc, extending perpendicular to the disc surface, are flanged in order to again achieve prestressing.

[0011] GB 2 394 289 A describes a force-sensitive device for measuring screw forces, in which a layer of force-sensitive material is arranged between two force-transmitting, disc-shaped elements. The force-sensitive layer is connected to an electrode on its top and bottom sides. A space between the two force-transmitting elements around the force-sensitive layer is filled with an additional material.

[0012] The object of the invention is to improve the state of the art.

[0013] The object is achieved by a washer for force measurement and force distribution when connecting a connecting means to a part to be connected, wherein the washer has a housing with an upper part and a lower part and a cavity inside the housing, and in the cavity a force sensor element is arranged and the force sensor element has at least one electrode and a dielectric, wherein at least one recess is arranged adjacent to the cavity in the housing in such a way that when an off-center force is introduced when connecting the connecting means to the part to be connected, the washer reproducibly deformable and the applied force can be reproducibly measured using the force sensor element.

[0014] This provides a force-measuring washer which is flat, rigid, and able to withstand overloads and is easy to manufacture. It is particularly advantageous that the geometric dimensions of the force-measuring washer according to the invention are essentially the same as the dimensions of a standard washer. This means that the force-measuring washer can be used directly instead of a conventional standard washer and enables the preload of a screw connection to be measured continuously both during assembly and in long-term operation. Consequently, even in existing systems, for example an offshore wind turbine, a conventional washer can be easily replaced with a force-measuring washer according to the invention. In addition, customer-specific component adaptation, for example by means of a chafing plate, is possible.Consequently, the force-measuring washer according to the invention can be used like a normal, standard washer, both in terms of its dimensions and its use.

[0015] The force-measuring washer distributes the force of a screw head evenly to the part to be connected as a base, ensures protection of the part to be connected from mechanical damage caused by the screw, especially during the screwing process, and provides a rigidity which is sufficiently high compared to the stiffness of the screw to ensure a secure screw connection. The torque during screwing is transferred to the base without damaging the force-measuring washer. The force-measuring washer is designed with a small number of joints or no joints at all to prevent settling or creep of the washer, as this could lead to a loss of preload and, consequently, failure of the screw connection.

[0016] This makes it possible to produce a force-measuring washer which, in terms of its geometric dimensions, particularly its height and outer diameter, is similar to standardised screw assemblies, as defined, for example, in accordance with DIN EN 14399, DIN 125 TI, DIN 125 T2, DIN 433 TI, DIN 433 T2, DIN 126, DIN 1440, DIN 1441 and / or DIN 7989. Accordingly, the force-measuring washer can be produced in all known screw connection sizes, for example from M8 to M36, preferably > M36.

[0017] For reference, a standard M30 washer is given, which has an outer diameter of 55 mm, an inner diameter of 31 mm and a height of 5 mm. When this standard washer is made of hot-dip galvanized steel, a calculated stiffness of 75 kN / pm results. The force-measuring washer according to the invention has the same inner and outer diameters and the same height as the standard M30 washer without a measuring function. Due to the force sensor element accommodated in the cavity of the housing, the stiffness of the force-measuring washer according to the invention is washer is only slightly lower, for example 50 kN / pm, than with the standard M30 washer. In return, the force-measuring washer according to the invention achieves a high overload capacity, which with a factor of 10x is in the range of the standard washer. In comparison to conventional load cells, for example with strain gauges, which with a height of 16 mm and an outer diameter of 72 mm are significantly higher than the height of 5 mm and the outer diameter of 55 mm of the force-measuring washer according to the invention and the standard M30 washer, the force-measuring washer according to the invention also significantly exceeds the low stiffness of 9.9 kN / pm and the low overload factor of 1.5x of the conventional force-measuring cell.

[0018] In addition, the force-measuring washer according to the invention offers the advantages of direct measurement of the screw preload force, the possibility of predictive maintenance, the determination of the remaining service life, and the ability to diagnose the condition of the screw connection even during operation. Furthermore, there is the option of sensor-integrated measurement data management and thus the evaluation of the measurement data directly in the force sensor element using a microprocessor and memory.

[0019] Due to the essentially space-neutral integration of the force sensor element, the component stiffness is, if at all, only slightly lower than that of a standard washer, and a high overload capacity with a factor of 10x of the nominal load range can be achieved.

[0020] The fact that at least one recess is arranged adjacent to the cavity within the housing, wherein the force sensor element is accommodated in the cavity, ensures that even when an eccentric force is introduced during screwing, the washer is reproducibly deformed and the introduced eccentric force is reproducibly measured by means of the force sensor element.

[0021] A key idea of ​​the invention is that a washer is designed directly as a force gauge in such a way that its geometric dimensions are identical or at least essentially the same as the corresponding standard washer through space-neutral integration of the force measuring sensor and that off-center measurement is also possible through the targeted spatial arrangement of at least one additional recess adjacent to the cavity in which the force sensor element is accommodated. Because the force-measuring washer does not have a separate measuring body, the number of joints and thus the setting behavior of the screw assembly is reduced and high rigidity and overload capacity are provided. By continuously recording the preload force during screwing, a low dispersion of the preload force can be achieved regardless of the tightening method (tightening factor 1.0).Due to the at least one recess adjacent to the cavity, slight load changes can be easily detected despite high preloads and a high. Sensitivity , for example of E = l , 96E- 07 mm, achievable .

[0022] The following terms are explained:

[0023] A “washer” is in particular an annular washer that can be pushed over a shaft of a fastener. During connection and in operation, the washer is arranged in particular between a screw head or a nut and a part to be connected. The washer is in particular a force-measuring washer and, in addition to transferring the force emanating from the underside of a screw head or a nut to a usually larger area of ​​a part to be connected, is also used to measure the preload force, introduced force and / or compressive force. The washer can also be integrated directly into a screw, for example if the screw has a larger and round head. The washer in particular has a larger outer diameter than the screw head or the nut.The washer is, in particular, a standardized washer and its dimensions comply with the above-mentioned DIN standards. For metal connections, the washer has, in particular, an outer diameter in a range of 1.8 to 2 times the bore diameter. For wood connections, the washer has, in particular, Outer diameter / bore diameter ratio of approximately 3:1. The washer has in particular a height in a range of 0.3 mm to 12 mm, depending on the standard size. Preferably, the height of the washer is Standard M30 washer in a range from 4.0 mm to 6.0 mm, preferably from 4.5 mm to 5.5 mm. The washer can be made of metal, such as brass, steel and / or stainless steel. The washer can also be hot-dip galvanized. The washer can also contain other metals, such as aluminum and / or copper. The washer can also contain plastic, for example polyamide, or be made entirely of plastic.

[0024] A “housing” is in particular a solid shell of the washer. The housing in particular has an upper part and a lower part. In the housing in particular there is a cavity on the inside for receiving the force sensor element. When connected, the upper side of the upper part is in particular in contact with the connecting means and the lower part rests with its underside on the part to be connected. In principle it should be emphasized that the terms upper part and lower part only serve to differentiate and the washer can in principle also be used rotated by 180° so that the lower part rests on the connecting means and the upper part rests on the connecting part when connected. The upper part can in particular be designed as a housing cover and the lower part as a housing base.The upper part and / or the lower part can also partially or completely form an inner wall of the washer on the inner diameter and / or an outer wall of the washer on the outer diameter. The upper part or the lower part is particularly suitable as a force introduction stamp. To prevent relative rotation and to ensure that the force sensor element is not damaged by the transmitted torque during assembly, the upper part is firmly connected to the lower part. The upper and lower parts can be connected, for example, by means of a press fit, laser welding, and / or a similar joining method. The upper and lower parts are made of metal, preferably stainless steel, and are therefore electrically conductive.

[0025] A “force sensor element” (also called a “force measuring sensor”) is in particular any type of sensor and / or measuring transducer by means of which an introduction of force can be measured. A force sensor element is in particular a pressure sensor. The force sensor element is preferably a capacitive pressure sensor which operates on the basis of a change in the electrical capacitance of at least one individual capacitor. When designed as a capacitive pressure sensor, the change in capacitance, in particular as a result of a bending of a membrane and / or a dielectric and the resulting change in a plate spacing of an electrical capacitor, for example designed as two electrodes, is evaluated as a sensor effect. In particular, the upper part or the lower part serves as one of the two electrodes of the capacitive pressure sensor.The force sensor element has, in particular, a height in a range from 0.30 mm to 1.50 mm, preferably in a range from 0.54 mm to 1.25 mm. The force sensor element has. in particular a surface area of ​​2.81 mm 2 up to 515.22 mm 2 or a sensor volume of 1.51 mm 3 up to 644.02 mm 3 A printed circuit board (PCB) or a multilayer film can be used as a semi-finished product for the force sensor element.

[0026] A "dielectric" is understood to mean, in particular, an electrically weak or non-conductive substance in which existing charge carriers are not freely movable. The dielectric is, in particular, formed as a solid. The dielectric is, in particular, an insulating material. The dielectric comprises, in particular, a plastic, for example, an elastomer. The dielectric comprises, for example, silicone, natural rubber, polyethylene, or LCP (liquid crystal polymer). The dielectric has, in particular, a height in a range from 0.01 mm to 0.40 mm, in particular from 0.04 mm to 0.25 mm, preferably from 0.1 mm to 0.20 mm. A layer of the dielectric is, in particular, arranged between the electrode and the housing and serves both for insulation and as a stop buffer and rigidity element.When the force-measuring washer is designed as a standard M30 washer, the dielectric has a surface area of ​​200 mm. 2 on.

[0027] An "electrode" is in particular an electron conductor. The electrode has in particular an electrical conductor, for example metal or graphite. The electrode interacts in particular with a counter electrode, wherein the counter electrode can be used as an upper part or lower part The electrode and / or the counterelectrode can also be formed as a metallization. The electrode is electrically insulated, in particular, from the housing of the washer. The electrode is preferably formed as a metallization on a printed circuit board (PCB). Alternatively, the electrode, together with the dielectric, can also be designed as a multilayer film.

[0028] Optionally, the washer can also comprise at least one electronic component for sensor-integrated digitization and / or data processing, a transmitter and / or a plug connection for external communication.

[0029] A "cavity" is, in particular, a recessed space inside the housing of the washer that is filled with the sensor force element. The force sensor element is, in particular, arranged with a precise fit in the cavity of the housing of the washer.

[0030] A "recess" is in particular an incision in an inner surface of the housing. The recess is preferably made internally in a surface of the upper part and / or the lower part. The at least one recess can also be arranged partially or completely in an inner wall around the cavity. Likewise, the at least one recess can be arranged at a transition between the inner wall of the cavity and the upper part or lower part. The washer can in particular have two or more recesses adjacent to the cavity have. The feature that “the at least one recess is arranged adjacent to the cavity in the housing” is understood to mean that the recess is formed directly adjacent to the cavity. The recess is therefore in direct contact with the cavity and the respective recess and the cavity form a cavity. The recess can have any shape, for example the recess is V-shaped, semicircular, circular or oval cut into the surface of the housing. However, the recess can also be rectangular, square, polygonal or curved. Likewise, the recess can be designed flexibly in addition to its shape, its size and dimensions.The recess is particularly designed such that, upon application of an off-center force, the washer and / or the dielectric deforms reproducibly, and the applied off-center force can be reproducibly measured by the force sensor element. The recess and / or recesses is / are filled with air.

[0031] In the case of a single recess, which is arranged externally at a radius R2 of the washer and whose distance da can be designed as the center of the washer to the center of the radius R2 and whose position can be designed as for the embodiment described below with two spaced-apart recesses, an introduced off-center force can also be measured reproducibly by means of the force sensor element. For this purpose, the single recess is designed with a reduced height Hda = H - R2, which represents the remaining material thickness of the washer between the recess R2 and an annular outer surface of the washer, where the height H is the constant material thickness between the cavity free of the recess and the annular outer surface of the washer. The reduced height Hda is set such that a stiffness at the radius at position R2 is equal to a stiffness at a radius at an inner position RI free of a recess on the cavity (RI equals zero compared to the embodiment described below with two spaced-apart recesses). In the case of the washer as a standard M30 washer, for example, H = 2.10 mm and R2 = 0.55 mm, so that the reduced height Hda = 1.55 mm with an identical stiffness of 243 kN / pm. This stiffness is particularly due to a very small volume of the force measuring sensor of 1.52 mm 3and a force sensor element height of only 0.6 mm. In the case of the washer as a standard M1 O washer, for example, H = 0.60 mm and R2 = 0.19 mm, so the reduced height Hda = 0.41 mm with the same stiffness of approximately 23 kN / pm.

[0032] Thus, with a single external recess, the volume is specifically reduced by this recess at position R2 in a range of 5.00% to 20.0% in order to at least reduce or completely eliminate the influence of an off-center force introduction during force measurement. In the case of the washer as a standard M30 washer, the percentage volume reduction of the solid material of the washer due to the single Recess at position R2, for example, 6.9%, for a standard M10 washer 10.0% and for a standard M36 washer 6.3%.

[0033] In a further embodiment of the washer, two radially spaced recesses are arranged adjacent to the cavity.

[0034] This allows the force sensor element to provide reproducible measurement values ​​even when precise centering of the components to be connected cannot be guaranteed due to fluctuating diameter tolerances of the screws and / or washer. Thanks to the two radially spaced recesses, the force-measuring washer and / or force sensor element is insensitive to off-center mounting.

[0035] The two radially spaced-apart recesses adjacent to the cavity are designed in the housing, the upper part, and / or the lower part in such a way that when a force is applied to the upper part or the lower part, the upper part or the lower part deforms reproducibly, regardless of the screw position and depending on the applied force. For this purpose, the upper part, as the part to which the force is applied, is preferably designed as a stamp.

[0036] To further increase the measuring accuracy, the two radially spaced recesses have different hollow volumes such that a the respective stiffness of the housing at the two radially spaced recesses is essentially the same.

[0037] To achieve a plane-parallel displacement of the force introduction stamp (upper or lower part), the radius RI of the first recess located further inside and the radius R2 of the second recess located further outside are designed so that the stiffness at position RI is identical to the stiffness at position R2. Ideally, the ratio of the distances between the radii of the two recesses is: da > R1(H - RI) ~di ~ R2(H - R2) where da = distance from the center of the washer to the center of radius R2, di = distance from the center of the washer to the center of radius RI and H = height of the washer.

[0038] Depending on the local stiffnesses to be set, the two radially spaced recesses have different hollow volumes.

[0039] In the case of the washer as a standard M30 washer, the inner recess has in particular a radius RI in a range from 0.0 mm to 2.0 mm, a maximum diameter in a range from 35.0 mm to 39.0 mm and a maximum height in a range from 1.5 mm to 2.7 mm. The outer recess has in particular a radius R2 in a range from 1.0 mm to 2.5 mm, a maximum diameter in a range from 40.0 mm to 46.0 mm and a maximum height in a range from 1.5 mm to 2.7 mm. The spatial position of the inner recess at position RI is in particular in a range from the distance di of 1.1 * ri < di < 1.2 * ri with ri equal to the inner radius of the washer, whereby the inner radius ri lies directly on the central bore diameter of the washer. The spatial position of the outer recess at position R2 is in particular in a range from the distance da of 0.8 * ra < da < 0.9 * ra with ra equal to the outer radius of the washer. For a standard M30 washer, for example, di = 36.95 mm and da = 50.06 mm.

[0040] The radius ratio R1 / R2 of the two recesses is preferably less than 1 in order to improve the reproducibility of the force sensor element in the event of an off-center force introduction.

[0041] Preferably, the inner recess has a smaller hollow volume than the outer recess. In particular, the measuring surface of the force sensor element lies substantially between the two recesses. If RI and R2 are equal, and thus also the wall thicknesses, the larger outer diameter of the outer recess would result in a larger section modulus and, consequently, greater rigidity. The larger section modulus is compensated by appropriately selecting the radius ratio and / or the hollow volume of the respective recess. so that the existing stiffnesses at both recesses are the same.

[0042] Basically, the overall stiffness results from the sum of the individual stiffness of the housing and the individual stiffness of the force sensor element. To increase the housing stiffness, the force sensor element is designed in such a way that the cavity in which the force sensor element is accommodated is minimized in terms of its height and diameter. The minimization of the cavity can be adjusted in particular via the height of the dielectric, the permittivity of the dielectric and / or the choice of the sensor element semi-finished product. The housing stiffness is adjusted by the width of the at least one recess and its position in the washer or the width and the radii RI and R2 of the two radially spaced recesses. The lower the height of the dielectric, the smaller the width of the respective recess and the radii RI and R2 that can be realized.

[0043] In principle, the washer is preferably designed to have the known mechanical properties of a conventional standard washer as closely as possible. In this regard, a small volume of the cavity for the force sensor element and a small volume of the recess or recesses are particularly advantageous, and accordingly, a single recess is preferred over two spaced-apart recesses.

[0044] In a further embodiment of the washer, the cavity is arranged in the upper part and / or between the upper part and the lower part.

[0045] When the cavity in which the force sensor element is accommodated is arranged in the upper part, the respective recess is preferably arranged in the underside of the upper part, directly adjacent to the cavity. Since the washer is symmetrical, the cavity can also be formed in the lower part instead of in the upper part, so that the respective recess is correspondingly introduced into the inner surface of the lower part. Likewise, the cavity can be formed between the upper part and the lower part, or partially in the upper part and partially in the lower part.

[0046] In order to improve the overload capacity of the force sensor element, the force sensor element is arranged at least laterally in the cavity in a force-locking and / or form-locking manner essentially transversely to an axial force direction.

[0047] Due to the force-locking and / or form-locking installation of the force sensor element in the cavity at least laterally and thus in the radial direction, occurring tensile loads are limited essentially transversely to the axial force direction, which occurs when the force sensor element is subjected to pressure during the force introduction. Due to the at least laterally flush fitting of the force sensor element in the cavity of the housing, an expansion in the transverse direction to the axial The direction of force and thus the tensile load on the components of the force sensor element are minimized. If the force sensor element is constructed with a multilayer film, a coefficient of friction between the force sensor element and the housing is sufficient. Optionally or additionally, the force sensor element can also be installed in the cavity on its top and / or bottom side in a force-fitting and / or form-fitting manner in the axial direction of force.

[0048] Thus, the axial force as well as bending and tilting moments, which are introduced as a distributed load on the outer surface of the upper part of the housing when the force is applied, can be transmitted from there via the force sensor element and forwarded to the lower part of the housing. As a result, the overload capacity of the housing is absorbed by the force sensor element, which acts as a stop.

[0049] The "axial force direction" is in particular the direction transverse to the diameter of the washer. The axial force direction is in particular also a direction along or parallel to the longitudinal central axis of the connecting means, for example a screw which is passed through the central opening of the washer. The "axial force direction" is in particular also the direction of force introduction in the connection case.

[0050] "Laterally substantially transverse to an axial force direction" means that the force sensor element with its inner and outer side walls is not exactly must be aligned perpendicular to the axial force direction and arranged in the cavity.

[0051] The term "positive locking" is understood in particular to mean that the two connection partners engage with one another. Thus, the engagement of the force sensor element and the inner wall or shape of the cavity prevents at least one lateral movement of the force sensor element. In a positive locking connection, for example, the active surfaces of the force sensor element and one inner wall of the cavity are subjected to surface pressure. In a positive locking connection, in particular the design of at least one inner wall of the cavity blocks the movement of the force sensor, or vice versa.

[0052] The term "force-locking" means that a normal force is exerted on the surfaces being connected to one another. The mutual displacement of an outer surface of the force sensor element and an inner surface of the cavity is prevented, in particular, as long as a counterforce acting due to static friction is not exceeded. In this case, the static friction between the active surfaces in particular causes the force sensor element to be displaced laterally into the cavity.

[0053] Thus, the positive and / or force-fitting connection between an outer surface of the force sensor element and the inner surface around the cavity prevents or at least reduces tensile strain of the force sensor element transverse to the axial force introduction direction.

[0054] In a further embodiment, the washer, in particular designed as a standard M30 washer, has a stiffness in a range from 30.0 kN / gm to 70.0 kN / gm, in particular from 40.0 kN / gm to 60.0 kN / gm, preferably from 45.0 kN / gm to 55.0 kN / gm.

[0055] This provides a force-measuring washer that has the stiffness of a conventional washer and only slightly lower or higher, for example, compared to a standard M30 washer with 75 kN / gm. These stiffness ranges apply in particular to a large volume of 644.0 mm 3 and a large height of 1.25 mm of the force sensor.

[0056] In order to form the upper part as a stamp and / or to specifically limit a tensile load on the force sensor element in a lateral, radial direction, the upper part partially or completely forms an outer side surface and / or an inner side surface of the washer.

[0057] In a further embodiment of the washer, the force sensor element has a height in a range of 5.0% to 40.0%, in particular from 10.0% to 30.0%, preferably from 15.0% to 25.0%, of a height of the washer and / or the washer has a height in a range of 90.0% to 110%, in particular from 95.0% to 105.0%, preferably from 98.0% to 102.0%, of a standard washer with the same outer diameter.

[0058] Thus, the clamped length of the Connection clamp package of an original and tested screw set.

[0059] To achieve the required stiffness and overload capacity, the dielectric has a relative permittivity in a range from 0.5 to 100.0, in particular from 1.0 to 80.0, preferably from 2.5 to 10.0.

[0060] The geometry, material, and thus the properties of the dielectric are tuned for the rigidity of the housing such that the rigidity of the dielectric is lower than the rigidity of the housing up to a certain value in a range of 30% to 80% of the washer's nominal load range. Within this range, the washer's housing thus contributes significantly to the system's rigidity. From this certain value in a range of 30% to 80% of the nominal load range up to the overload range, the dielectric transfers an increasing proportion of the force to the housing base, thereby preventing permanent deformation of the washer and, consequently, destruction of the force sensor element.

[0061] In a further embodiment of the washer, the dielectric has a modulus of elasticity in a range from 0.2 MPa to 12,000 MPa, in particular from 30.0 MPa to 5,000 MPa, preferably from 60.0 MPa to 1,500 MPa.

[0062] This allows the stiffness of the force sensor element and thus the overall stiffness of the washer to be adjusted via the E-modulus of the dielectric. The higher the Young's modulus of the dielectric, the lower the strain of the force sensor element when a force is applied in the axial direction, and consequently, the higher the stiffness of the force sensor element. For a dielectric made of LCD (Liquid Crystal Polymer) with an Young's modulus of 11,700, the strain in the direction of force is 0.19 mm when designed as an M30 standard washer. For a dielectric made of natural rubber with an Young's modulus of 64.5, the strain in the direction of force is already 34.88 mm.

[0063] The "relative permittivity" of the dielectric (also called dielectric constant) is, in particular, the dimensionless ratio of the permittivity of the dielectric to the permittivity of a vacuum. The permittivity generally indicates, in particular, the polarization ability of a material by electric fields. The permittivity, in particular, indicates the electrically insulating material property of the dielectric.

[0064] The "elastic modulus" (also called E-modulus) describes the proportional relationship between stress and strain during the deformation of the dielectric, particularly in the case of linear elastic behavior. The elastic modulus increases particularly with the resistance that a material and / or the dielectric offers to its electrical deformation. The higher the elastic modulus, the stiffer the dielectric.

[0065] Optionally, the washer can have an additional electronic component, for example, to transmit the measurement data from the force sensor element to an external data processing unit using RFID or other wireless communication. A digitization and evaluation unit can also be integrated directly into the force sensor element or into the washer. Likewise, the washer can have a plug connection on its outer circumference for reading data and for communication. In this case, the electronic component and / or the plug connection can protrude radially outwards beyond the outer diameter of the washer in a small area of ​​the circumference.

[0066] By communicatively connecting the force-measuring washer to an external data processing and evaluation system and / or a cloud-based condition monitoring system, the provided measurement data can be used for temporal trend analyses, targeted monitoring of structural loads and / or mechanical operating loads, calculation of the remaining service life of the system in which the force-measuring washer is used, and / or for predictive maintenance planning. This reduces service and maintenance costs and avoids unplanned maintenance work. It also enables early damage detection and damage progression assessment to determine the optimal maintenance interval. Consequently, unplanned downtimes, for example in offshore wind turbines, are minimized.

[0067] The invention is explained in more detail below using exemplary embodiments. Figure 1 is a highly schematic three-dimensional Illustration with a cross section through a force-measuring washer, Figure 2 is a highly schematic sectional view of an alternative force-measuring washer without a force sensor in the cavity, Figure 3 is a highly schematic sectional view of the force-measuring washer from Figure 2 mounted between a screw head of a screw and a base, Figure 4 is a highly schematic sectional view of another alternative of the force-measuring washer from Figure 3 with an electrical component and a plug connection, Figure 5 is a schematic, three-dimensional Representation of the alternative washer from Figure 3 in cross section and top view, and Figure 6 is a highly schematic three-dimensional Presentation of the alternative of Washer from Figure 3 in side view from above.

[0068] A force-measuring washer 101 has an upper part 103 with an upper side 105 and a lower part 107 with a lower side 109, each made of stainless steel. The upper part 103 completely forms a lateral outer side wall 129. An inner side wall 131 is partially formed by the upper part 103 and the lower part 107. The upper part 103 and the lower part 107 are welded together and form the housing of the force-measuring washer 101. A cavity 111 is introduced into the upper part 103 inside the force-measuring washer 101. Directly adjacent to the cavity 111, an inner recess 125 is formed in an inner side wall of the lower part 107 around the cavity 111, and an outer recess 127 is formed in an inner surface of the upper part 103. The inner recess 125 and the outer recess 127 are filled with air.A force sensor 113 is arranged flush in the cavity 111 and is laterally clamped between the inner side walls of the upper part 103 and the lower part 107.

[0069] The force sensor 113 has an electrode 115, which is arranged on a dielectric 117, as well as a printed circuit board 119. The electrode 115 and the dielectric 117 are designed as a multilayer foil. The dielectric 117 serves as an insulator with respect to the electrode 115 and as a stop buffer and stiffness element. Furthermore, the force-measuring washer 101 has an electronic component 121 for sensor-integrated digitization and Data processing, wherein the electronic component is arranged within the lower part 107 (see Figure 1).

[0070] The force-measuring washer 101 has an outer diameter of 55 mm and an inner diameter of 31 mm as well as a height of 5 mm and thus corresponds in dimensions to an M30 standard washer.

[0071] The force-measuring washer 101 is pushed with its inner free diameter over the shaft of a screw (not shown in Figure 1), and the screw is screwed into a base (likewise not shown) (see Figure 3). Due to manufacturing tolerances, force is applied slightly off-center to the upper side 105 of the upper part 103 during screwing, with a force of 450 kN being applied. Due to the radially spaced inner recess 125 and the outer recess 127, which have approximately the same rigidities, the force sensor 113 reproducibly measures the applied force despite the slightly off-center force application. The compressive force causes deformation of the dielectric 117, and as a result, a change in the distance between the electrode 115 and a second metallization applied to the circuit board 119.Thus, a force-measuring washer 101 is provided which enables high overall rigidity, high overload capacity and reproducible pressure measurement by means of the force sensor 113.

[0072] In an alternative shown in Figure 2, a force-measuring washer has a similar structure to described above. However, the inner recess 125 and the outer recess 127 adjacent to the cavity 111 are both made in the underside of the upper part 103 (Figure 2 shows the cavity 111 without the force sensor 113). The inner recess 125 and the outer recess 127 are semicircular in cross-section. The outer recess 127 has a larger hollow volume than the inner recess 125 in order to provide approximately the same rigidity at the respective center of the respective recess 125, 127. The cavity 111 is also formed completely in the upper part 103 here. The upper part 103 is again designed as a force introduction stamp and completely occupies the outer side wall 129 and partially the inner side wall 131 of the force-measuring washer 101. Furthermore, the force-measuring washer 101 has a force sensor 113 with a circuit board 119 as described above (see Figure 3).In a short area on the outer side wall 129, the printed circuit board 119 breaks through the outer side wall 129 and has a plug connection for external communication, not shown in detail in Figure 3.

[0073] Figure 3 shows the force-measuring washer 101 from Figure 2 in an assembled state, in which a screw 141 presses with its screw head onto the upper side 105 of the upper part 103 of the force-measuring washer 101 and the underside 109 of the lower part 107 of the force-measuring washer 101 rests on a base 143. In the assembled state, a continuous measurement of the compressive force on the force-measuring washer 101 and thus allows long-term monitoring of the screw connection.

[0074] In a further alternative of the force-measuring washer 101 shown in Figures 4 to 6, the lower part 107 forms an outer side wall 129 and the upper part 103 completely forms the inner side wall 131. In this alternative, the inner recess 125 is formed next to the force sensor 113 and thus as a lateral extension of the cavity 111, while the outer recess 127 is formed between the lower part 107 and the upper part 103. As described above, the washer 101 has a force sensor 113 with a printed circuit board 119 which partially breaks through the outer side wall 129 in a short area and there has a plug connection 123 for external communication (Figures 5 and 6). Furthermore, the washer 101 has an electronic component 121 for measured value acquisition and evaluation.Thus, when using the force-measuring washer 101 in an offshore wind turbine, the stored measured values ​​from the force-measuring washer 101 can be read out by the electronic component 121 by connecting an external laptop to the plug connection 123.

[0075] Thus, force-measuring washers 101 are provided which have the same dimensions as the corresponding standard washer and thus enable the use of conventional screw assemblies, wherein the force-measuring washers provide high rigidity, high overload capacity and high measuring accuracy. Reference symbol list 101 Force-measuring washer 103 Top 105 Top 107 Bottom 109 subpage 111 Cavity 113 Force sensor 115 electrode 117 dielectric 119 circuit board 121 electronic component 123 plug connection 125 inner recess 127 outer recess 129 Exterior wall 131 inside wall 141 Screw 143 Document

Claims

Patent claims:

1. Washer (101) for force measurement and force distribution when connecting a connecting means (141) to a part (143) to be connected, wherein the washer (101) has a housing with an upper part (103) and a lower part (105) and a cavity (111) located inside the housing, and a force sensor element (113) is arranged in the cavity (111), and the force sensor element (113) has at least one electrode (115) and a dielectric (117), characterized in that at least one recess (125, 127) is arranged adjacent to the cavity (111) in the housing such that when an off-center force is introduced when connecting the connecting means (141) to the part (143) to be connected, the washer (101) can be reproducibly deformed and the introduced force can be measured by means of the force sensor element (113) is reproducibly measurable.

2. Washer (101) according to claim 1, characterized in that two radially spaced recesses (125, 127) are arranged adjacent to the cavity (111).

3. Washer (101) according to claim 1 or 2, characterized in that the two radially spaced recesses (125, 127) have different Hollow volume such that a respective rigidity of the housing at the two radially spaced recesses (125, 127) is substantially the same.

4. Washer (101) according to one of the preceding claims, characterized in that the cavity (111) is arranged in the upper part (103) and / or between the upper part (103) and the lower part (107).

5. Washer (101) according to one of the preceding claims, characterized in that the force sensor element (113) is arranged at least laterally in the cavity (111) in a force-fitting and / or form-fitting manner substantially transversely to an axial force direction.

6. Washer (101) according to one of the preceding claims, characterized in that the washer (101), in particular designed as a standard M30 washer, has a rigidity in a range from 30.0 kN / pm to 70.0 kN / pm, in particular from 40.0 kN / pm to 60.0 kN / pm, preferably from 45.0 to 55.0 kN / pm.

7. Washer (101) according to one of the preceding claims, characterized in that the upper part (103) partially or completely forms an outer side surface (129) and / or an inner side surface (131) of the washer (101).

8. Washer (101) according to one of the preceding claims, characterized in that the force sensor element (113) has a height in a range of 5.0% to 40.0%, in particular from 10.0% to 30.0%, preferably from 15.0% to 25.0% of a height of the washer (101) and / or the washer (101) has a height in a range of 90.0% to 110%, in particular from 95.0% to 105.0%, preferably from 98.0% to 102.0%, of a standard washer with the same outer diameter.

9. Washer (101) according to one of the preceding claims, characterized in that the dielectric (117) has a relative permittivity in a range from 0.5 to 100.0, in particular from 1.0 to 80.0, preferably from 2.5 to 10.

0.

10. Washer (101) according to one of the preceding claims, characterized in that the dielectric (117) is a Elastic modulus in a range from 0.2 MPa to 12,000 MPa, in particular from 30.0 MPa to 5,000 MPa, preferably from 60.0 MPa to 1,500 MPa.

Images