Measuring nut

Abstract

The invention relates to a method of determining a dimensional change of a measurement nut (100), wherein the measurement nut comprises a contact portion (102) and a non-contact portion (104), the contact portion (102) being adapted for attachment to an object, such as a bolt or a screw, the contact portion and the non-contact portion being positioned coaxially but axially offset with respect to each other. The method comprises attaching at least a part of the contact portion to the object, the non-contact portion being free of direct contact with the object; exposing the object to an external load, thereby causing a dimensional change of the contact portion of the measurement nut; and determining the dimensional change of the measurement nut by means of a measurement at the non-contact portion. The invention further relates to a measurement nut (100) and a measurement system (200) comprising the measurement nut.

Description

Technical Field

[0001] The invention relates to a method for determining a dimensional change of a measuring nut. The invention further relates to a measuring nut and a measuring system comprising the measuring nut. Background Art

[0002] In mechanical systems, it may sometimes be of interest to determine the tension caused by a force applied to an object, such as torque or axial tension.

[0003] Conventional techniques for measuring tension can measure tension on the object itself. A sensor is then fastened to the object to be measured, and an electrical coupling is then established between the sensor and the analysis electronics. This has disadvantages, such as the need to maintain the electrical coupling with suitable quality over time. The sensor can be, for example, a strain gauge. However, strain gauges are quite expensive and difficult to use in real-world settings. Consequently, they are not particularly well-suited for conventional settings. They require calibration before measurement to obtain reliable measurements. Strain gauges are typically glued to the object to be measured. However, the glue is often unstable over time, and recalibration is therefore necessary to obtain reliable measurements over time.

[0004] In some prior art solutions, the tension is instead determined by means of a measuring nut which is attached to the object, for example by being screwed onto a threaded object such as a screw. The tension in the object is derived from the measurement on the measuring nut.

[0005] Patent document US2006 / 0225511A1 discloses a device for measuring prestress in a bolt / nut connection. The device comprises a screw-nut provided with a sensor device for sensing prestress. The nut has a standard design, and the nut itself constitutes the sensor body, being located within its outer peripheral surface. At least one recess is machined into the nut, into which a sensor is placed. The sensor is adapted to sense mechanical stress in the nut and to provide a signal representative of the stress for transmission to an external recording device. However, by providing the nut with a machined recess, the nut itself is weakened, which negatively affects its mechanical properties.

[0006] When measuring the tension of an object, it is desirable to measure as accurately as possible. Furthermore, it is desirable that the measurement be easy and quick to perform. It is also desirable that it should be possible to perform the measurement while the object is in its intended position (e.g., in construction, i.e., not in a test stand).

[0007] Furthermore, it is desirable that the load bearing capacity and life characteristics of the measuring nut are not negatively affected by the provided weakening, for example the recess as disclosed in US 2006 / 0225511 A1. Summary of the Invention

[0008] It is an object of the present disclosure to overcome or ameliorate at least one disadvantage of the prior art, or to provide a useful alternative.

[0009] The above objects are achieved by the subject matter of the independent claims. Variants of the invention are set out in the dependent claims, in the following description and in the drawings.

[0010] Thus, according to a first aspect of the present invention, a method for determining a dimensional change of a measuring nut is provided, wherein the measuring nut comprises a contact portion and a non-contact portion, the contact portion being adapted to be attached to an object, such as a bolt or a screw, the contact portion and the non-contact portion being positioned coaxially but axially offset relative to each other.

[0011] The method includes:

[0012] - attaching at least a portion of the contact portion to the object, the non-contact portion not being in direct contact with the object,

[0013] - exposing the object to an external load, thereby causing a dimensional change of the contact portion of the measuring nut, and

[0014] - Determine the dimensional change of the measuring nut by measuring at the non-contact portion.

[0015] The dimensional change of the measuring nut is caused by the tension to which it is exposed, which in turn is a result of the external load applied to the object. In other words: when an object is exposed to an external load, the external load induces tension in the object, and thus also in the measuring nut via the contact portion that is in direct contact with the object. Therefore, the external load will cause dimensional changes in both the contact portion and the non-contact portion. By measuring at the non-contact portion of the measuring nut rather than at the contact portion, the non-contact portion can be used to amplify the dimensional change of the contact portion. Experiments have shown that amplifications of up to 10-25 times are possible. Therefore, compared to prior art solutions where the measuring nut is in full contact with the object (as in the device of US2006 / 0225511A1) or measurements are taken at the object itself, the dimensional change of the measuring nut and, thus, the tension in the object can be measured with greater accuracy.

[0016] The tensioned state of the measuring nut measured at the non-contact portion as described herein can be compared to measurements of the untensioned state or measurements at a known tension to establish the dimensional change. This is further described below.

[0017] The object is typically a mechanical component, such as a bolt or screw or any other mechanical component that may be exposed to tension. The object may include an external threaded portion. The mechanical component may form part of a fastening device. Furthermore, tension may be desired to determine the load-bearing structure. Thus, the object may be part of another larger entity, such as a device, machine or vehicle.

[0018] The external load applied to the object may be a tensile force, a compressive force, a compressive force, a shear force, a torsional force, a bending force, a force caused by gravity, a force resulting from a temperature difference, or any combination of such forces. Such forces are known to induce tension in the object, which can be determined using the method for determining the dimensional change of the measuring nut, using the measuring nut, and using the measuring system described herein.

[0019] The contact portion of the measuring nut is suitable for attachment to an object. Therefore, the contact portion can be threaded, for example, provided with an internal thread surrounding the inner hole. In that case, the internal thread of the contact portion is typically intended to be attached to a corresponding external thread of the object to be measured. Alternatively or in addition, the contact portion can be attached to the object by means of any other means, for example by welding, press fit, one or more clamps, one or more clips, adhesive or a combination thereof. When the contact portion is attached to the object, i.e., when it is in direct contact with the object, for example via the thread, the non-contact portion remains without any direct contact with the object. However, the non-contact portion is in indirect contact with the object via the contact portion. Therefore, the non-contact portion can change its size independently of the object. The non-contact portion can, for example, be offset axially from the object.

[0020] Measurements can be performed on the top surface of the non-contact portion. At least a portion of this surface faces in the axial direction of the measuring nut. Measuring at the top surface can be beneficial when limited space around the measuring nut makes access to one or more side surfaces difficult. If measuring at the top surface, a single measurement may be sufficient, preferably at or around the longitudinal axis of the measuring nut. The term "top surface" refers to the surface located at the top of the non-contact surface. Depending on how the measuring nut is attached to the object, the top surface can face in any direction, such as downward.

[0021] Measuring at the top surface can be advantageous when the measuring nut is a capped nut that includes a capping portion incorporated into the non-contact portion of the measuring nut. In that case, the measurement is typically performed at the top surface of the capping portion, preferably at or about the longitudinal axis of the measuring nut. If capped, the measuring nut is preferably positioned such that the non-contact portion is axially offset from the object.

[0022] As an alternative or in addition to measuring at the top surface, measurements can be performed at at least one side surface of the non-contact portion (e.g., at two or three side surfaces). Measuring at at least one side surface may be beneficial when the space around the top surface of the measuring nut is limited and inaccessible.

[0023] Measurements can be performed on every side surface of the measurement nut. If measurements are not performed on every side surface, it is typically beneficial to select the side surfaces to be measured so that they are not adjacent to each other and are evenly distributed around the circumference of the measurement nut. A typical nut includes six side surfaces, as does a typical measurement nut. Thus, measurements can be performed, for example, on all six side surfaces, on three side surfaces spaced 120 degrees apart, or on two opposing side surfaces spaced 180 degrees apart. If measurements are performed on side surfaces, it may be beneficial to measure on more than one side surface to capture any asymmetric dimensional changes of the measurement nut.

[0024] The contact portion of the measuring nut can include a threaded first portion and a threaded second portion, with the non-contact portion positioned between the threaded first and second portions of the contact portion, wherein the measurement is performed at the non-contact portion between the threaded first and second portions of the contact portion. Preferably, the measurement is performed midway between the threaded first and second portions of the contact portion. This aspect of the method is advantageous when the object is a rod (e.g., a screw), where the side of the measuring nut is accessible from the side of the rod. In this case, when the rod is exposed to an external load, the measuring nut will follow the axial movement of the rod.

[0025] The method may include attaching the measuring nut to the object so that the axial length of the non-contact portion is in the range of 25%-3000% of the axial length of the portion of the contact portion that is in direct contact with the object, for example 50%-1000% or 50%-500% or 50%-250% or 75%-125%.

[0026] Typically, the entire axial length of the contact portion of the measuring nut is in direct contact with the object. By making the same axial length in direct contact for each measurement, it can be determined that the measuring nut is attached in a corresponding manner for each measurement, making it possible to compare measurements taken at different tensioning states of the measuring nut.

[0027] The measurement can be performed in a measuring recess provided in the non-contact portion, preferably, the measurement is performed in a measuring recess provided at the top surface and / or at least one side surface of the non-contact portion. The measuring recess can be provided at multiple side surfaces of the non-contact portion, for example at two, three or all side surfaces of the non-contact portion. The measuring recess can be provided at each side surface of the non-contact portion. The measuring recess can typically have a circular cross-section. The depth of the measuring recess is preferably adapted to the size of the measuring nut. Typically, the depth is at least 1 mm, preferably at least 4 mm, but a depth of up to 20 mm may occur. The measuring recess can be utilized to protect the pattern, as described in more detail below.

[0028] As an alternative or in addition to using a measurement recess when performing measurements, measurements can be performed in a through-hole provided in the non-contact portion. Preferably, the measurement hole is provided on the top surface and / or at least one side surface of the non-contact portion. The measurement hole can typically have a circular cross-section.

[0029] The measuring recess and / or measuring hole weakens the mechanical strength of the non-contact portion, which helps amplify dimensional changes in the measuring nut when measuring at the non-contact portion. Furthermore, the measuring recess and / or measuring hole provide a suitable docking location for the sensor unit. This allows for easy docking in a similar manner and with high accuracy for each measurement.

[0030] The dimensional change can be determined using a sensor unit comprising a sensor from the following group: a strain gauge, a capacitive sensor, a capacitance sensor, a thermal conductivity sensor, a piezoresistive sensor, a piezoresistive capacitive sensor, a photodiode-based sensor, an ultrasonic sensor, a pressure sensor, an organic thin-film transistor sensor, an optical sensor, a 3D scanner, a ruler, a caliper, a micrometer, a feeler gauge, or a combination of sensors comprising at least one of these sensors. The sensor can be of the type commonly used for fingerprint detection, such as in smartphones. The sensor can be an array sensor, which can include a plurality of sensors as described herein. The sensor unit forms part of a measurement system. The sensor unit is typically connected to the analysis unit by wire or wirelessly. The sensor unit can also include a processor and / or a memory for storing the measured data. The sensor unit can further include an indicator light and / or a display.

[0031] The sensor unit can be adapted to interface with the measuring nut. In particular, the sensor unit can be adapted to interface with the measuring recess and / or measuring hole disclosed herein. Thus, the sensor unit can be of sufficient size and shape to fit neatly within the measuring recess or measuring hole.

[0032] The measurement can be performed using a pattern included in the non-contact portion or in the object. The pattern can include circles, lines, or dots. The pattern can be positioned in a measuring recess on the measuring nut. In this case, the measuring recess will help protect the pattern from accidental damage.

[0033] The pattern can be positioned on the surface of the non-contact portion or object. The pattern can also be protected, for example, by a protective surface coating (e.g., paint) or a protective covering. In any case, the pattern is detectable from the outside of the non-contact portion or object. Thus, the sensor unit can, for example, detect the pattern via the protective coating or covering, which can be, for example, electrically non-conductive and / or thermally non-conductive. Thus, the protective coating or covering is selected to function appropriately with the sensor unit.

[0034] The pattern may be macroscopic, so that it is visible to the naked eye. Typically, the pattern may have a maximum extension of at least 0.01 mm, preferably at least 0.1 mm, more preferably at least 1 mm, the maximum extension being determined in the plane in which the pattern or its projection (if non-flat) extends. If the pattern comprises a circle, the maximum extension is the diameter, which may be in the range of 3-10 mm or 4-8 mm.

[0035] The pattern may be inherent or provided on at least a portion of the surface of the non-contact portion of the measuring nut or on the object.

[0036] An inherent pattern exists on the non-contact portion without any additional processing or application, such as a natural surface structure or a pattern integrally formed on at least a portion of the non-contact portion or on the object as a result of manufacturing the component.

[0037] If provided, a pattern can be provided for the purpose of performing the measurement. Providing a pattern can include applying one or more patterns to the non-contact portion or object. The pattern can be applied to the non-contact portion or object, for example, by printing, laser gravure printing, mechanical gravure printing, etching, drilling, milling, turning, sputtering, or electrical discharge machining. The pattern can be an applied surface structure, similar to knurling. Alternatively, the pattern can be provided on a separate film that is permanently or non-permanently attached to the non-contact portion or object, for example as a printed pattern on a plastic or metal film, which is glued to the non-contact portion or object or attached by means of at least one mechanical fastener.

[0038] The pattern may be provided for another primary purpose besides determining tension, but regardless, the pattern may be useful for determining tension. Examples of such patterns are QR codes, bar codes, or printed patterns, such as text or numbers. Such patterns may be applied to the non-contact portion or object by any of the methods described herein.

[0039] Another example of providing a pattern for another primary purpose than determining tension is when the object is provided with an external thread detectable by a sensor unit that interfaces with a measuring hole of a non-contact portion of a measuring nut.

[0040] The pattern may comprise a plurality of pattern elements. The pattern may be regular or irregular. A regular pattern is repetitive, i.e., the pattern repeats pattern elements. An example would be a pattern comprising a plurality of dots, i.e., the dots are repeating pattern elements with preselectable distances between them. The pattern may comprise a variety of different pattern elements. The term regular means that when the pattern is in an untensioned state, it corresponds to an untensioned state corresponding to a non-contact portion. The pattern elements may have a predefined depth and / or a predefined height, for example, the pattern elements are indentations or protrusions.

[0041] The pattern may include one or more grooves. It has been found to be beneficial to use circular grooves. If measured at the top surface, the grooves may be centered around the length axis. Multiple concentric circular grooves may be used.

[0042] The pattern can be represented as different material properties, for example, where the pattern elements are regions with different conductive properties. In that case, the pattern can include indentations filled with insulating material, while the rest of the pattern is conductive, i.e., insulating "islands" in a "sea" of conductive material, or vice versa.

[0043] The pattern can be used to obtain a reference for determining the dimensional change of the measuring nut. This reference can then be determined by determining the distance between the pattern elements in the untensioned state of the measuring nut. The reference can also be determined in the tensioned state of the measuring nut, where a force of known magnitude and direction of application is applied to the measuring nut.

[0044] The pattern can include a code that is unique to the measuring nut to which the pattern is located, thereby providing a unique identification for the measuring nut. The code can be readable using an encryption key, for example, provided as an algorithm in an analysis unit included in a measuring system that also includes the measuring nut and the sensor unit. If the identification of the measuring nut is known, further information about the measuring nut, such as tension characteristics, can be linked to this specific measuring nut via the identification. This further information can be stored in a database, for example, in the cloud.

[0045] The pattern can be formed so that, in the untensioned state of the measuring nut, the pattern elements have known distances between them, which can be used as a reference for data analysis. However, it is not necessary to store reference data for the purpose of determining dimensional changes. However, storing reference data may be of interest anyway, as it may reveal differences in the measuring nut over time.

[0046] As an alternative or in addition, the pattern determined by the sensor unit itself can be used as a reference to determine the distance between pattern elements by exploiting the fact that the induced tension acts mainly in a certain direction and therefore mainly affects the distance between pattern elements in a first direction and leaves the distance between pattern elements more or less unaffected in a second direction (e.g. perpendicular to the first direction), or by analyzing the relationship between pattern elements.

[0047] Alternatively or additionally, the reference information may be included in the pattern itself, for example as information points included in the pattern, e.g., information about the positions of pattern elements or the distances between pattern elements when in an untensioned or tensioned state, wherein a force of known magnitude and known direction of application has been applied to at least a portion of the measuring nut. Alternatively or additionally, the pattern may include information about the tension properties of the non-contact portion, i.e., information about its reaction to various tension forces.

[0048] The pattern can be positioned in one or more of the measurement recesses described herein. This reduces the risk of inadvertently damaging the pattern compared to a non-contact portion without any measurement recess.

[0049] The method may include:

[0050] - determining the pattern by means of an array sensor (e.g. an image acquisition device),

[0051] - Use image analysis to derive dimensional information from the pattern.

[0052] Array sensors are typically two-dimensional. Image analysis can then be used to determine whether the object is subjected to high or even excessive loads, such as torsion. It can further be determined whether the load is centered or eccentric.

[0053] The non-contact portion of the measuring nut may include at least one slot extending at least partially in the axial direction of the measuring nut, preferably 1-10 slots, more preferably 2-6 slots, and most preferably 3-5 slots. The at least one slot is configured to increase the dimensional change of the non-contact portion caused by the contact portion. Thus, the slot(s) may be configured to amplify the dimensional change occurring in the contact portion of the measuring nut during measurement, thereby improving measurement accuracy.

[0054] The method may further comprise:

[0055] - a reference measurement at a non-contact portion with a known tension in the measuring nut, and

[0056] - Reference measurement is used when determining the dimensional change of the measuring nut.

[0057] The state of known tension in the measuring nut is preferably the untensioned state. This measurement can be performed by the manufacturer of the measuring nut. The reference measurement only needs to be performed once. It can then be associated with the unique identification of the specific measuring nut, for example, via a pattern as described herein. Therefore, the measuring nut can be provided with an identifier, such as an applied number, a barcode, or a QR code.

[0058] Alternatively or additionally, the reference measurement can be performed in a state of known tension of the measuring nut, different from an untensioned state in which a force of known magnitude and known application direction has been applied to the measuring nut.

[0059] In some practical measurement situations, the geometry is not ideal, for example due to misalignment of the measuring nut relative to the object to which it is attached (e.g. a bolt). For example, the measuring nut and the object may have non-parallel axes or non-parallel surfaces. This may be due to dirt and / or paint on the surfaces. Other causes may be errors that occur during the manufacture and / or installation of the measuring nut or the object. For bolt joint applications, such misalignment is sometimes referred to as joint face angulation. As a consequence, the object and the measuring nut will be loaded asymmetrically, resulting in large local tensions. This problem may ultimately be detrimental to the object and / or to the measuring nut, since the large local tensions may affect the fatigue strength in a negative way.

[0060] Thus, if the interest is in determining possible misalignment or angulation of the joint faces, the method may further comprise:

[0061] - Determining the extent of the asymmetric change of the determined dimensional change of the measuring nut.

[0062] This can be performed, for example, by calculations used in mathematical curve fitting methods such as the method of least squares, the method of moments, or the method of maximum likelihood.

[0063] The degree of asymmetric change is considered relative to an ideal measurement, for example, assuming that the surfaces are parallel and / or the axes are aligned. Thus, a low degree of asymmetric change is obtained when the measurement result of the tensioned state of the measurement situation has approximately the same overall shape as the measurement result of the untensioned state, but in a slightly smaller proportion. Ideally, the measurement result of the tensioned state has the same overall shape as the measurement result of the untensioned state, but in a slightly smaller proportion. However, if the measurement result of the tensioned state has another overall shape, such as a skew, it is called an asymmetric change. The difference between the two measurement results can be determined using mathematical curve fitting methods (such as the method of least squares, the method of moments or the method of maximum likelihood). Comparison can also be made with known measurement results of known tension states or with known nominal dimensions of the pattern.

[0064] If the degree of asymmetry change is high, this is a sign that the object is not correctly installed. This can be exploited in the method by setting a threshold level for the acceptable degree of asymmetry change. If the determined degree of asymmetry change exceeds the threshold level, an operator performing, for example, a bolted joint application, can be warned of misalignment by the measurement system (e.g., by a warning system included in the measurement system). The operator can then loosen the object, such as a bolt, and make some adjustments, such as adjusting washers, before re-tightening the object.

[0065] In that case, the method may further comprise:

[0066] - comparing the determined degree of asymmetry change with a preselectable threshold level,

[0067] And optional steps:

[0068] - sending a warning, such as an acoustic, visual and / or tactile warning, when the determined degree of asymmetry change exceeds a preselectable threshold level.

[0069] According to a second aspect of the present invention, a measuring nut is provided. The measuring nut includes a contact portion and a non-contact portion. The contact portion is adapted to be attached to an object, such as a bolt or a screw. The contact portion and the non-contact portion are positioned coaxially with respect to each other but axially offset. The measuring nut is provided with a measuring region at the non-contact portion. The measuring region is adapted to determine a dimensional change of the measuring nut when attached to the object.

[0070] The measuring nut according to the present invention can be used when performing the method disclosed herein. The measurements described in the method are then performed at the measuring area of ​​the measuring nut. Therefore, the details described herein for the method also apply to measuring nuts. Furthermore, the advantages described herein for the method also apply to measuring nuts, and vice versa.

[0071] While the contact portion is attached to an object, i.e., in direct contact with it, the non-contact portion remains free of any direct contact with the object. Therefore, the non-contact portion can change its dimensions independently of the object. For example, the non-contact portion can be axially offset from the object. As mentioned above, the contact portion of the measuring nut can be threaded. In that case, it is suitable for attachment to the threaded portion of the object.

[0072] The measurement region can be positioned on the top surface of the non-contact portion. Alternatively or additionally, the measurement region can be positioned on at least one side surface of the non-contact portion, for example, two or three side surfaces. Details and advantages of different positioning methods are described in conjunction with the above methods.

[0073] The contact portion of the measurement nut can comprise a threaded first portion and a threaded second portion, the non-contact portion being positioned between the threaded first portion and the threaded second portion of the contact portion. Thus, the measurement zone is positioned between the threaded first portion and the threaded second portion of the contact portion. Preferably, the measurement zone is positioned in the middle between the threaded first portion and the threaded second portion of the contact portion. The threaded first portion and the threaded second portion are connected to each other via the non-contact portion. This can be beneficial when the object is a rod, for which the side portions are easily accessible from the side of the rod. In this case, when the rod is exposed to an external load, the measurement nut will follow the axial movement of the rod, which can be measured as a change in dimension at the measurement zone.

[0074] The non-contact portion can comprise at least one rod, e.g. two or three rods, spanning between the threaded first portion and the threaded second portion. There can further be at least one side portion comprised in the non-contact portion, e.g. two or three side portions with a respective side surface. The at least one side portion can e.g. be separated in the middle by a slot of the kind described herein. The measurement zone can be positioned in the side portions, e.g. such that it is separated by the slot.

[0075] Alternatively, the non-contact portion of the measurement nut can comprise a first portion and a second portion, between which a threaded contact portion can be positioned. In that case, the measurement can be performed at either or both of the first portion or the second portion of the non-contact portion.

[0076] The non-contact portion of the measurement nut according to the present invention can be unthreaded, as it is not intended to be in direct contact with the object. However, in some embodiments, it is easier to provide threads for both the contact portion and the non-contact portion during manufacturing of the measurement nut, although the threads of the non-contact portion are not intended to be used.

[0077] The non-contact portion can comprise at least one slot, preferably 1-10 slots, more preferably 2-6 slots, most preferably 3-5 slots, extending in the axial direction. The slot(s) can be used to amplify the change in dimension that occurs in the contact portion of the measurement nut, thereby improving the accuracy of the measurement.

[0078] The at least one slot can extend at least 40%, preferably at least 60%, more preferably at least 80%, most preferably at least 95% of the axial length of the non-contact portion in the axial direction. It can extend over the entire length of the non-contact portion.

[0079] The at least one slot may extend in the radial direction by at least 80%, preferably at least 90%, more preferably at least 95%, and most preferably 100% of the radial extension of the non-contact portion. Thus, the non-contact portion may be divided into subsections by the slots. If the non-contact portion comprises a centrally hollow hole, the radial extension of the slot is measured as the wall thickness.

[0080] The at least one slot typically has an open end. Alternatively, both ends may be open or both ends may be closed. The appropriate width of the slot depends on the size of the measuring nut, but is typically in the range of 1-5 mm.

[0081] The non-contact portion may have an axial length in the range of 10-100 mm. The non-contact portion may have an axial length in the range of 25%-3000% of the axial length of the contact portion, for example 50%-1000% or 50%-500% or 50%-250% or 75%-125%.

[0082] The measurement area may include a measurement recess and / or a through-going measurement hole. For details and advantages of the measurement recess and / or the through-going measurement hole, please refer to the description of the first aspect.

[0083] The measurement area can include a pattern, either inherent or imposed, such as a groove. The pattern can include circles, lines, or a dot pattern. The pattern can be positioned within the measurement recess. For further details and advantages regarding the pattern, see the description of the method.

[0084] The measuring nut can be provided with a unique identifier, which provides a unique identification for the measuring nut. For further details and advantages of the unique identification, please refer to the description of the method.

[0085] According to a third aspect of the present invention, a measuring system is provided, comprising: a measuring nut as described herein; a sensor unit adapted to interface with the measuring nut to determine a dimensional change of a non-contact portion of the measuring nut by measuring at or with the aid of a measuring region; and an analysis unit adapted to determine the dimensional change of the measuring nut from the determined dimensional change of the non-contact portion. The sensor unit and the analysis unit may be combined into a single unit.

[0086] The measurement system according to the present invention can be used when performing the method disclosed herein. Therefore, the details described herein for the method can also be applied to the measurement system. In addition, the advantages described herein for the method are also valid for the measurement system, and vice versa.

[0087] The sensor unit may include a sensor from the following group: a strain gauge, a capacitive sensor, a capacitance sensor, a thermal conductivity sensor, a piezoresistive sensor, a piezoresistive capacitive sensor, a photodiode-based sensor, an ultrasonic sensor, a pressure sensor, an organic thin-film transistor sensor, an optical sensor, a 3D scanner, a ruler, a caliper, a micrometer, a feeler gauge, or a combination of at least one of these sensors. The sensor may be of the type commonly used for fingerprint detection, such as in smartphones. The sensor may be an array sensor that may include multiple sensors as described herein. Because the non-contact portion amplifies the dimensional change of the measuring nut, the requirements for the sensor may be lower than in prior art measurement systems. Alternatively, the amplification of the dimensional change may be used to improve the accuracy of the measurement.

[0088] The sensor unit may comprise an array sensor, such as an image acquisition device, and the analysis unit may be adapted for image analysis. The array sensor is typically two-dimensional. Image analysis may then be used to determine whether the object is subject to high or even excessive torsion. It may also be possible to determine whether the load is centered or eccentric.

[0089] In a measurement system where the measuring nut includes a through-hole, the sensor unit can be adapted to interface with the through-hole. Thus, the sensor unit can be of sufficient size and shape to fit neatly within the hole. This is suitable for measuring a pattern positioned on an object.

[0090] The analyzing unit of the measuring system may be adapted to determine the degree of asymmetric change of the determined dimensional change of the measuring nut. This may be performed, for example, by calculations used in mathematical curve fitting methods (eg, the method of least squares, the method of moments, or the method of maximum likelihood).

[0091] The analyzing unit of the measuring system may be adapted to compare the extent of the asymmetry change with a preselectable threshold level.

[0092] The measuring system may further comprise a warning system adapted to send a warning, such as an acoustic, visual and / or tactile warning.In case the extent of the asymmetry change exceeds a preselectable threshold level, the warning is problematic.

[0093] If the degree of asymmetry change is high, this is a sign that the object is not correctly installed. Therefore, if the determined degree of asymmetry change exceeds a threshold level, an operator performing the bolt joint application can be warned of misalignment by the measurement system (e.g., by a warning system included in the measurement system). The operator can then loosen the object and make some adjustments, such as adjusting washers, before re-tightening the object. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] The invention will be further explained hereinafter by means of non-limiting examples with reference to the accompanying drawings, in which:

[0095] Figures la-le A measuring nut according to a first embodiment of the present invention is shown.

[0096] Figure 2 A measuring system according to one embodiment of the present invention is shown.

[0097] Figure 3 A method of determining a dimensional change of a measuring nut according to one embodiment of the present invention is shown.

[0098] Figure 4a Exemplary patterns are shown.

[0099] Figure 4b A representation of the measurement results is shown.

[0100] Figures 5a-5d A measuring nut according to a second embodiment of the invention is shown.

[0101] Figures 6a-6c A measuring nut according to a third embodiment of the present invention is shown.

[0102] Figure 7 A measuring nut according to a fourth embodiment of the present invention is shown.

[0103] Figures 8a-8b A measuring nut according to a fifth embodiment of the present invention is shown.

[0104] Figure 9a Shown is a representation of measurement results applied to a bolted joint in an aligned measurement situation.

[0105] Figure 9b Shown is a representation of measurement results for a bolted joint application in a misaligned measurement situation.

[0106] Figure 9c Show Figure 9a Side view of a bolted joint application being measured in .

[0107] Figure 9d Show Figure 9a Cross-section of a bolted joint application measured in .

[0108] Figure 9e Shown in Figure 9b Side view of a bolted joint application being measured in .

[0109] Figure 9f Shown in Figure 9b Cross-section of a bolted joint application measured in .

[0110] Figure 10aA screw is shown provided with a measuring zone.

[0111] Figure 10b A flange is shown provided with a measuring zone.

[0112] It should be noted that the drawings are not necessarily to scale and that the dimensions of some features of the application can have been exaggerated for the sake of clarity. DETAILED DESCRIPTION

[0113] The application will be illustrated below by means of examples. It will be appreciated, however, that the inclusion of the examples is for the purpose of illustrating the principles of the application and not for limiting the scope of the application as defined by the appended claims. Details from two or more of the examples can be combined with each other.

[0114] Figures la-le A measuring nut 100 according to a first embodiment of the application is shown. Figure la A perspective view is shown, Figure lb A top view is shown, Figure lc A side view is shown, Figure Id A cross-sectional view is shown taken along the line A-A in Figure lb while a cross-sectional view is shown taken along the line B-B in Figure le A cross-sectional view is shown taken along the line B-B in Figure lc A cross-sectional view is shown taken along the line B-B in

[0115] The measuring nut 100 comprises a threaded contact portion 102 suitable for being attached to an object (not shown), and a non-contact portion 104. The object is typically a mechanical part, such as a bolt or a screw or any other mechanical part.

[0116] The measuring nut 100 has an axial direction with a length axis A. The contact portion 102 and the non-contact portion 104 are positioned coaxially, i.e. around the same length axis A, but axially offset relative to each other, with the non-contact portion 104 in the shown perspective view on top of the contact portion 102. The measuring nut 100 is provided with a measuring zone 106 at a top surface 108 of the non-contact portion 104. The measuring zone 106 comprising a measuring recess 110 in the shown embodiment is suitable for determining a dimensional change of the measuring nut 100 when attached to an object.

[0117] The dimensional change of the measuring nut 100 is caused by the tension to which it is exposed, which in turn is a result of the external load applied to the object. In other words, when an object is exposed to an external load, the external load induces tension in the object, and thus also in the measuring nut 100 via the contact portion 102, which is in direct contact with the object. Therefore, the external load will cause dimensional changes in the contact portion 102 and also in the non-contact portion 104. By measuring at the non-contact portion 104 of the measuring nut 100 rather than at the contact portion 102, the non-contact portion 104 can be used to amplify the dimensional change of the contact portion 102. Experiments have shown that amplification of up to 10-25 times is possible. Therefore, compared to prior art solutions that measure at the contact portion of the measuring nut or at the object itself, the dimensional change of the measuring nut 100, and thus indirectly measure the tension in the object, can be measured with higher accuracy.

[0118] The measuring nut 100 is formed as Figure 2 A portion of a measuring system 200 is shown. The measuring system 200 further comprises a sensor unit 210 adapted to interface with the measuring nut 100 to determine a dimensional change of the non-contact portion 104 of the measuring nut 100 by measuring at the measuring region 106, and an analysis unit 220 adapted to determine a dimensional change of the measuring nut 100 from the dimensional change determined at the non-contact portion 104.

[0119] The sensor unit 210 may include a sensor from the following group: a strain gauge, a capacitive sensor, a capacitance sensor, a thermal conductivity sensor, a piezoresistive sensor, a piezoresistive capacitive sensor, a photodiode-based sensor, an ultrasonic sensor, a pressure sensor, an organic thin film transistor sensor, an optical sensor, a 3D scanner, a ruler, a calliper, a micrometer, a feeler gauge, or a combination sensor including at least one of these sensors. The sensor may be of the type commonly used for fingerprint detection, such as in smartphones. The sensor may be an array sensor that may include a plurality of sensors as mentioned herein.

[0120] like Figure Id As best seen in the figure, the contact portion 102 is internally threaded. The internal threads 112 are intended to be attached to corresponding external threads on the object to be measured. In the illustrated embodiment, the non-contact portion 104 is unthreaded. It is not intended to come into direct contact with the object. However, it is sometimes easier to provide threads for both the contact portion 102 and the non-contact portion 104 during manufacture of the measuring nut 100, although in that case, the threads of the non-contact portion 104 are not intended for attachment.

[0121] In the shown first embodiment, the measuring nut 100 is a cover nut comprising a cover portion 114 forming a cover of the non-contact portion 104. This is best seen in Figure Id The measuring zone 106 with its measuring recess 110 is positioned in the cover portion 114.

[0122] The measuring nut 100 is provided with four slots 116a-d evenly distributed around the circumference of the non-contact portion 104. In the shown embodiment, the slots 116a-d extend axially through the entire axial length of the non-contact portion 104, see Figure la and Figure lc and have an open end facing upwards. The slots 116a-d extend radially through the non-contact portion 104, see Figure la , Figure lb and Figure le In the cover portion 114, the slots 116a-d extend through the entire radius. In the lower portion 118 of the non-contact portion 104, i.e. below the cover portion 114, the slots 116a-d extend through the entire wall thickness. Thus, the slots 116a-d divide the non-contact portion 104 into four sub-portions 120a-d. When measured at the measuring zone 106, the slots 116a-d are used to amplify the size change of the contact portion 102.

[0123] The sensor unit 210 is intended to be docked to the measuring zone 106 provided with a pattern in the form of circular grooves 122, as best seen in Figure la and Figure lb The circular grooves 122 are centred around the length axis A. They are positioned in the measuring recess 110.

[0124] Figure 3 A method 300 of determining a size change of a measuring nut 100 according to one embodiment of the present application is shown. The method 300 comprises:

[0125] 310: Attaching at least a portion of the contact portion 102 to an object, the non-contact portion 104 having no direct contact with the object,

[0126] 320: Exposing the object to an external load, thereby causing a size change of the contact portion 102 of the measuring nut 100, and

[0127] 330: Determining the size change of the measuring nut 100 by a measurement at the non-contact portion 104.

[0128] The measurement can be performed with the measuring system 200 shown in Figure 2 When using a similar measuring system as shown in Figures la-leWhen the measuring nut 100 is measured, the measurement is performed at the top surface 108 of the measuring nut 100. Thus, the sensor unit 210 is docked with the measuring recess 110 forming the measuring area 106. In other embodiments, see, for example, the following description Figures 5a-5d 、 Figures 6a-6c 、 Figure 7 as well as Figures 8a-8b In an embodiment of the present invention, the measurement is instead performed at one or more side surfaces of the measuring nut 500 , 600 , 700 , 800 .

[0129] The sensor unit 210 may include an array sensor, such as an image acquisition device, which is typically two-dimensional and has an analysis unit 220 suitable for image analysis.

[0130] Method 300 may further include the optional steps of:

[0131] 305 : A reference measurement is performed at the non-contact portion 104 under a known tension state of the measuring nut 100 .

[0132] In that case, the reference measurement may be used when determining the change in the size of the measuring nut 100 in step 330 .

[0133] The known tension state of the measuring nut 100 is preferably an untensioned state.

[0134] Alternatively or additionally, the reference measurement may be performed in a state where the known tension of the measuring nut 100 differs from the untensioned state in which a force of known magnitude and known application direction has been applied to the measuring nut 100 .

[0135] If step 305 is omitted, known information about the pattern can be used, e.g. Figures la-le The nominal radius of the circular groove 122 of the measuring nut 100 is .

[0136] Figure 4a An exemplary pattern is shown, which is shown as Figures la-le The circular groove 122 of the measuring nut 100 . Figure 4b An exemplary representation of measured data is shown. The solid line shows the measurement result for circular groove 122 in an untensioned state (i.e., 0 Nm). The scale is given in pixels of the image acquisition device, where 1 pixel is 0.05 mm. Therefore, for the untensioned circular groove 122 of the measuring nut 100 of the exemplary embodiment, the radius is approximately 4 mm.

[0137] When the contact portion 102 of the measuring nut 100 is tensioned, the radius of the circular groove 122 located in the non-contact portion 104 will decrease as the thread 112 comes into contact with the object stretching the contact portion 102, as indicated by Figure 4b, which represents the applied torque of 500 Nm, which induces tension in the object and, therefore, in the measuring nut 100. By comparing the dotted 500 Nm measurement result with the solid line measurement result of the untensioned state, the dimensional change of the non-contact portion 104 can be measured, and thus the dimensional change of the measuring nut 100 can be determined. Thereafter, the tension in the object can be deduced from the measured dimensional change.

[0138] Figures 5a-5d Another measuring nut 500 according to a second embodiment of the present invention is shown. Figure 5a Showing a perspective view, Figure 5b Showing a side view, Figure 5c Shown along Figure 5b The cross-sectional view is taken along line BB in FIG. Figure 5d Shown along Figure 5b A cross-sectional view taken along line DD in FIG.

[0139] The measuring nut 500 has a hexagonal cross section and includes six side surfaces 508a-508f. It includes a threaded contact portion 502 and a non-threaded non-contact portion 504. It has a through hole 514.

[0140] The measuring nut 500 has three measuring areas 506a, 506b, 506c located at respective side surfaces 508a, 508c, 508e 120 degrees apart. Each measuring area 506a-506c includes a measuring recess 510a, 510b, 510c. The measuring areas 506a-506c include a pattern formed by circular grooves 522.

[0141] Measuring nut 500 is provided with three slots 516a, 516b, and 516c extending through the entire axial length of non-contact portion 504. These slots also extend through the entire wall thickness of non-contact portion 504. Thus, they divide non-contact portion 504 into three subsections 520a-520c. Furthermore, slots 516a-516c extend through the respective measuring areas 506a-506c, dividing them in half and dividing circular recess 522 into two semicircular shapes.

[0142] Figures 6a-6c Yet another measuring nut 600 according to a third embodiment of the invention is shown, which is suitable for attachment to, for example, a screw. Figure 6a Showing a perspective view, Figure 6b Showing a side view, Figure 6c Another side view is shown, which is Figure 6b The side view is 90 degrees.

[0143] The contact portion 602 of the measuring nut 600 comprises a threaded first portion 602a and a threaded second portion 602b, between which a non-contact portion 604 is positioned. (The threads are not shown in Figure 6a The axial length of the contact portion 602 is the sum of the axial lengths of the threaded first portion 602a and the threaded second portion 602b. The threaded first portion 602a and the threaded second portion 602b are connected to each other via the non-contact portion 604. The non-contact portion 604 comprises two stems 624a, 624b spanning between the threaded first portion 602a and the threaded second portion 602b. The non-contact portion 604 further comprises two side portions 626a, 626b having respective side surfaces 608a, 608b. The side portions 626a-626b are divided in the middle by respective slots 616a, 616b. The slots 616a-616b are thus open at both ends.

[0144] There are two measuring zones 606a, 606b, each comprising a measuring recess 610a, 610b. They are positioned in the side portions 626a, 626b between the threaded first portion 602a and the threaded second portion 602b, in the shown embodiment, in the middle between the threaded first portion 602a and the threaded second portion 602b. The positioning at the side portions 626a, 626b makes the measuring zones 606a-606b accessible from the side of the stem. When the stem is exposed to an external load, the measuring nut 600 will follow the axial movement of the stem, which movement can be measured as a change in size at the measuring zones 606a, 606b. The measuring zones 606a, 606b can comprise a pattern not shown, e.g. a circular groove 122, 522 similar to the embodiments of Figures la-le and Figures 5a-5d .

[0145] Figure 7 The fourth embodiment of the measuring nut 700 shown in Figures 5a-5dThe second embodiment shown shares many features. It includes a threaded contact portion 702 and a non-contact portion 704. Instead of a measurement area formed by measurement recesses 510a-510c as in the second embodiment, the non-contact portion 704 is provided with a measurement area formed by three through-holes 724a-724c. These serve as docking locations for the sensor unit 210 of the measurement system 200. When docked in one of the measurement holes 724a-724c, the sensor unit 210 tracks the displacement of the non-contact portion 704, which in turn is caused by the object being tensioned. Because the holes 724a-724c are through-holes, the sensor unit 210 can use a pattern provided on the object to determine changes in the measurement dimensions of the nut 700. If the object includes external threads, the pattern can be threads, or the object can be intentionally provided with a pattern detectable through the holes 724a-724c, such as a QR code, barcode, or dot pattern. The holes 724a-724c may be provided at at least one side surface. Figure 7 It is shown at three side surfaces in FIG, preferably evenly distributed around the periphery. It would also be possible to have measuring recesses, for example similar to those described for the first to third embodiments.

[0146] Figures 8a-8b Yet another measuring nut 800 according to a fifth embodiment of the present invention is shown. Figure 8a shows a perspective view, and Figure 8b A cross-sectional view is shown.

[0147] Measuring nut 800 includes a threaded contact portion 802 and an unthreaded non-contact portion 804. Non-contact portion 804 includes a first portion 804a and a second portion 804b, with contact portion 802 positioned between first portion 804a and second portion 804b of non-contact portion 804. The axial length of non-contact portion 804 is the sum of the axial lengths of first portion 804a and second portion 804b.

[0148] The non-contact portion 804 is provided with a measurement area in the form of measurement holes 824a-824f extending through the side surface. Alternatively, a measurement recess, such as that described for the first to third embodiments, may be provided. In the illustrated embodiment, there are three measurement holes 824a-824c in the first portion 804a, and three measurement holes 824d-824f in the second portion 804b. For comments regarding the positioning of the side surfaces, see the notes for the second, third, and fourth embodiments. For comments regarding the measurement holes 824a-824f, see the notes for the fourth embodiment.

[0149] Figure 9a and Figure 9bTwo further examples of measurements made on a pattern comprising circular grooves 122 similar to Figures la-le The circular groove of the measuring nut 100 is also Figure 4a Shown in. Figure 9a and Figure 9b The solid line measurement results show the measurement results of the circular groove 122 in the untensioned state, that is, under 0 Nm. The radius is then about 4 mm, as can be collected on the y scale. Its pattern is Figure 9a and Figure 9b The measuring nut 100 shown in FIG. 1 should be engaged with an object, such as, for example, a bolt 124 or a screw, in Figures 9c-f Shown is a bolted joint application.

[0150] Similar to Figure 4b In the example shown in FIG. 1 , when the contact portion 102 of the measuring nut 100 is tightened, the radius of the circular groove 122 located in the non-contact portion 104 will decrease. Figure 9a and Figure 9b , which is shown by the dashed measurement result, representing an applied torque of 500 Nm, which causes tension in the object and thus in the measuring nut. By comparing the dashed measurement result of 500 Nm with the solid measurement result of the untensioned state, the dimensional change of the non-contact portion can be measured, and thus the dimensional change of the measuring nut 100 can be determined. Thereafter, the tension in the object can be deduced from the measured dimensional change. The low values ​​of the measurement results at approximately 0°, 90°, 180° and 270° correspond to the four slots 116a-116d provided in the measuring nut 100, see Figures la-le .

[0151] Figure 9a A measurement example is shown for which the 0 Nm and 500 Nm measurement results are roughly symmetrical, i.e. the 500 Nm measurement result has the same overall shape but a slightly smaller radius, illustrating an ideal measurement situation. This is the desired measurement situation, as Figures 9c-f As shown in Figure 9c shows a side view, and Figure 9d Shown along Figure 9c Note that Figures la-le In contrast, the measuring nut 100 is positioned upside down, with the top surface 108 of the non-contact portion 104 facing downward. The washer 126 is held between the end surface 128 of the contact portion 102 and the lower surface 130 of the head 132 of the bolt 124. In this example, the upper surface 134 and the lower surface 136 of the washer 126 are parallel to each other. Thus, the bolt 124 is positioned in a straight and aligned manner relative to the measuring nut 100. Thus, the 500 Nm measurement is inside the 0 Nm measurement over the entire circumference, as shown in FIG. Figure 9a As seen in.

[0152] However, sometimes in actual situations, the upper surface 134' and the lower surface 136' of the gasket 126' are not parallel to each other, such as Figures 9e-f As shown in Figure 9e shows a side view, and Figure 9f Shown along Figure 9e FF. This could be due to dirt and / or paint on the surface. Other causes could be errors during the manufacture and / or installation of the bolt 124' or the washer 126'. This misalignment in bolted joint applications is sometimes referred to as angularity. As a result, the bolt 124' and the gauge nut 100 will be loaded asymmetrically, generating large local tensions. Ultimately, this problem can be detrimental to the bolted joint application, as the large local tensions can negatively impact fatigue strength.

[0153] This actual measurement situation is Figure 9b , which shows that the 500Nm measurement is asymmetric. From about 0° to about 90°, and from about 180° to about 270°, the 500Nm measurement is inside the 0Nm measurement, however, Figure 9a There is a larger difference between the two measurements compared to the ideal case. From about 90° to about 180°, and from about 270° to about 360°, the 0 Nm and 500 Nm measurements are almost on top of each other.

[0154] The degree of asymmetry change can be quantified to detect the degree of misalignment, also known as angulation of the joint faces, that occurs in bolted joint applications. The degree of asymmetry change is considered relative to an ideal result, for example, assuming that the surfaces are parallel. Thus, a low degree of asymmetry change is obtained when the measurement result in the tensioned state has approximately the same overall shape as the measurement result in the untensioned state, but similar Figure 9a Ideally, the tensioned measurement has the same overall shape as the untensioned measurement, but at a slightly smaller scale. However, if the tensioned measurement has another overall shape, e.g. Figure 9b If it is shown as skewed in the figure, it is called an asymmetric change.

[0155] As an example only, for Figure 9a and Figure 9b The measurements performed in FIG. 1 are shown with an applied torque of 500 Nm. The measurement result determined in the tensioned state can be compared with the measurement result in the untensioned state or the nominal radius of the circular groove 122. From this, the difference between the two measurement results can be determined using a mathematical curve fitting method (e.g., the method of least squares, the method of moments, or the method of maximum likelihood). Figure 9a and Figure 9bThe measurement results are quantified using standard deviation to quantify the difference from the 0 Nm measurement result, which is first determined and stored for comparison.

[0156] If the degree of asymmetry change is high, this is a sign of incorrect installation of the bolted joint application. This can be used in the method 300 of determining the dimensional change of the measuring nut 100 by setting a threshold level for the degree of asymmetry change that is acceptable. If the determined degree of asymmetry change exceeds the threshold level, the operator performing the bolted joint application can be warned of misalignment by the measuring system 200, e.g. by the warning system 230 comprised in the measuring system 200, see Figure 2 . The operator can then loosen the bolted joint application and make some adjustments, e.g. adjusting the washers, before redoing the bolted joint application.

[0157] Thus, if it is of interest to determine misalignment or joint face angling, the method 300 described herein, see Figure 3 , can further comprise the optional step of:

[0158] 340: determining the degree of asymmetry change of the determined dimensional change.

[0159] Additionally, the method 300 can comprise the steps of:

[0160] 350: comparing the determined degree of asymmetry change with a preselactable threshold level, and

[0161] 360: sending a warning if the determined degree of asymmetry change exceeds the preselactable threshold level.

[0162] The warning can be audible, visual and / or tactile. It can be sent by the warning system 230 comprised in the measuring system 200, see Figure 2 , which e.g. together with the analysis unit 220 is located as a single integral unit. There can e.g. be a beeping sound, the light can change colour and / or blink, or the tool used for tensioning the measuring nut 100 can vibrate. Thus, the warning system 230 can comprise one or more LEDs and / or a loudspeaker.

[0163] Even though the measurement of misalignment or joint face angling has been exemplified above by the pattern in the form of the circular recess 122, it would be possible to use other patterns, e.g. similar to the other patterns described herein. The measuring nut can further be of any type described herein.

[0164] Furthermore, corresponding measurements can be made on other types of connections (e.g. screw connections) in order to detect misalignment or joint face angulation. The measurement of misalignment or joint face angulation can be performed with the aid of a measuring nut 100, as shown, but can also be performed on, for example, bolts, screws, threaded rods, washers or spacers.

[0165] Furthermore, it may be relevant to measure the extent of asymmetric changes for any element in which dimensional changes, for example caused by external loads, may occur. Examples of such elements are bolts, screws, threaded rods 1002 (see Figure 10a ), gasket, spacer or flange 1004 (see Figure 10b ). The external load applied to the element may be a tensile force, a pressing force, a compressive force, a shear force, a torsional force, a bending force, a gravity force, a force caused by a temperature difference or any combination of such forces. It is known that such a force causes tension in the element, which can be determined using a method corresponding to the method for determining a dimensional change of a measuring nut as described herein and / or with the aid of a measuring system 200 as described herein. Thus, when determining a dimensional change, the measurement can reveal the degree of asymmetric change, which indicates some kind of misalignment or irregularity of the measured element. Thus, by arranging one or more measuring areas 1006; 1008, 1010, 1012 in the elements 1002, 1004, or with the aid of a separate component attached to the element, similar to the measuring nut described herein, the degree of asymmetric change can be detected directly in the element (for example in the screw 1002 or in the flange 1004).

[0166] Methods for measuring the degree of asymmetry change of an element may include:

[0167] - determining the dimensional changes of the elements 1002 , 1004 by measurements at measurement zones 1006 ; 1008 , 1010 , 1012 provided in the elements,

[0168] - The degree of asymmetry change is determined from the determined dimensional change.

[0169] The element may be, for example, a nut, a measuring nut, a bolt, a screw, a threaded rod, a washer, a spacer or a flange.

[0170] The step of determining the extent of the asymmetry change may be performed, for example, by calculations used in mathematical curve fitting methods such as the method of least squares, the method of moments or the method of maximum likelihood.

[0171] The dimensional change may be caused intentionally by including in the aforementioned optional steps the method for measuring the degree of asymmetric change of an element:

[0172] - exposing the component to external loads, thereby causing dimensional changes in the component.

[0173] Additionally, the method for measuring the degree of asymmetry change of an element may include the following steps:

[0174] - comparing the determined degree of asymmetry change with a preselectable threshold level,

[0175] - If the extent of the determined asymmetry change exceeds a preselectable threshold level, sending a warning.

[0176] The method for measuring the degree of asymmetry change of an element may further comprise:

[0177] - determining a pattern contained in the measurement zone by means of an array sensor (eg an image acquisition device), and

[0178] -Use image analysis to derive dimensional information from the pattern.

[0179] The method for measuring the degree of asymmetry change of an element may further comprise:

[0180] - a reference measurement at a known tension on the element, and

[0181] - Reference measurements are used when determining dimensional changes in components.

[0182] The details given for the method described herein for determining a dimensional change of a measuring nut, for the measuring nut described herein and for the measuring system described herein also relate to the method for measuring the degree of asymmetric change of a component, as they are applicable.

[0183] Further modifications of the present invention are possible within the scope of the appended claims. As such, the present invention should not be considered to be limited by the embodiments and drawings described herein. Instead, the full scope of the present invention should be determined by the appended claims with reference to the specification and drawings.

Claims

1. A method for determining a dimensional change of a measuring nut (100), the measuring nut (100) comprising a contact portion (102) and a non-contact portion (104), the contact portion (102) being adapted to be attached to an object, the contact portion (102) and the non-contact portion (104) being positioned coaxially but axially offset relative to each other, the measuring nut (100) being provided with a measuring area (106) positioned at a top surface (108) of the non-contact portion (104), The method comprises: - attaching (310) at least a portion of the contact portion (102) to the object, the non-contact portion (104) not being in direct contact with the object, - exposing (320) the object to an external load, thereby causing a change in the dimensions of the contact portion (102), and - determining the dimensional change (330) of the measuring nut (100) by means of a measurement performed at the measuring zone (106) of the non-contact portion (104), The method is characterized in that: The non-contact portion (104) of the measuring nut (100) includes at least one slot (116a-116d) extending at least partially in the axial direction (A) of the measuring nut (100), and the at least one slot (116a-116d) is used to increase the dimensional change of the non-contact portion (104) caused by the contact portion (102). The method according to claim 1 , wherein the object is a bolt or a screw.

3. The method according to claim 1, wherein the non-contact portion (104) of the measuring nut (100) comprises 1-10 slots extending at least partially in the axial direction (A) of the measuring nut (100).

4. The method according to claim 1, wherein the non-contact portion (104) of the measuring nut (100) comprises 2-6 slots extending at least partially in the axial direction (A) of the measuring nut (100).

5. The method according to claim 1, wherein the non-contact portion (104) of the measuring nut (100) comprises 3-5 slots extending at least partially in the axial direction (A) of the measuring nut (100).

6. The method according to claim 1, wherein the measuring nut (100) is a cover nut including a cover portion (114), the cover portion (114) being included in the non-contact portion (104) of the measuring nut (100).

7. The method according to any one of claims 1 to 6, wherein the measurement is performed in a measuring recess (110) provided at the top surface (108) of the non-contact portion (104), and / or the measurement is performed at or around the length axis of the measuring nut (100).

8. The method according to claim 7, wherein the measuring recess (110) has a depth in the range of 1 to 4 mm.

9. The method according to any one of claims 1 to 6, wherein the dimensional change is determined by means of a sensor unit (210), the sensor unit (210) comprising a sensor from the following group: a strain gauge, a capacitive sensor, a capacitance sensor, a thermal conductivity sensor, a piezoresistive sensor, a piezoresistive capacitive sensor, a photodiode-based sensor, an ultrasonic sensor, a pressure sensor, an organic thin film transistor sensor, an optical sensor, a 3D scanner, a ruler, a caliper, a micrometer, a feeler gauge or a combination sensor comprising at least one of these sensors.

10. The method of claim 9, wherein the sensor is an array sensor.

11. The method according to claim 1 , wherein the measuring is performed by means of a pattern comprised in the non-contact portion ( 104 ) or in the object, the pattern being inherent or provided, and wherein the method comprises: - determining said pattern by means of an array sensor, - Using image analysis to derive dimensional information from the pattern.

12. The method of claim 11, wherein the pattern comprises grooves (122, 522). The method according to claim 11 , wherein the array sensor is an image acquisition device.

14. The method according to any one of claims 1 to 6, wherein the method further comprises: - determining (340) the extent of the asymmetric change of the determined dimensional change of the measuring nut (100) by means of a mathematical curve fitting method.

15. The method according to claim 14, wherein the mathematical curve fitting method is the least squares method, the moment method or the maximum likelihood method.

16. The method of claim 14, wherein the method further comprises: - comparing the determined degree of asymmetry change with a preselectable threshold level (350), and: - sending (360) a warning when the determined degree of asymmetry change exceeds said preselectable threshold level.

17. The method of claim 16, wherein the warning is an audible, visual and / or tactile warning.

18. Measuring nut (100), comprising: - a contact portion (102) adapted to be attached to an object, and - Non-contact part (104), The contact portion (102) and the non-contact portion (104) are positioned coaxially but axially offset relative to each other, in: The measuring nut (100) is provided with a measuring area (106) positioned at a top surface (108) of the non-contact portion (104), the measuring area (106) being adapted to perform measurement at the measuring area (106) by determining a change in the size of the measuring nut (100) attached to the object, The measuring nut is characterized in that: The non-contact portion (104) includes at least one slot (116a-116d) extending in the axial direction (A) of the measuring nut (100).

19. The measuring nut (100) according to claim 18, wherein the object is a bolt or a screw.

20. The measuring nut (100) according to claim 18, wherein the non-contact portion (104) includes 1-10 slots extending in an axial direction (A) of the measuring nut (100).

21. The measuring nut (100) according to claim 18, wherein the non-contact portion (104) includes 2-6 slots extending in the axial direction (A) of the measuring nut (100).

22. The measuring nut (100) according to claim 18, wherein the non-contact portion (104) includes 3-5 slots extending in the axial direction (A) of the measuring nut (100).

23. The measuring nut (100) according to claim 18, wherein the measuring nut (100) is a cover nut including a cover portion (114), and the cover portion (114) is included in the non-contact portion (104) of the measuring nut (100).

24. The measuring nut (100) according to any one of claims 18 to 23, wherein the non-contact portion (104) is non-threaded.

25. The measuring nut (100) according to any one of claims 18 to 23, wherein the measuring region (106) comprises a measuring recess (110).

26. The measuring nut (100) according to claim 25, wherein the measuring recess (110) has a depth in the range of 1 to 4 mm.

27. The measuring nut (100) according to any one of claims 18 to 23, wherein the measuring area (106) comprises a pattern, the pattern being inherent or imposed.

28. The measuring nut (100) of claim 27, wherein the pattern comprises grooves (122, 522).

29. The measuring nut (100) according to claim 27, wherein the pattern comprises circles, lines or a dot pattern.

30. A measurement system (200), comprising: - A measuring nut (100) according to any one of claims 18 to 29, a sensor unit (210) adapted to interface with the measuring nut (100) to determine a dimensional change of the non-contact portion (104) of the measuring nut (100) by measuring at or with the aid of the measuring region (106), and An analyzing unit (220) adapted to determine the dimensional change of the measuring nut (100) from the determined dimensional change of the non-contact portion (104).

31. The measuring system (200) according to claim 30, wherein the sensor unit (210) comprises a sensor from the following group: a strain gauge, a capacitive sensor, a capacitance sensor, a thermal conductivity sensor, a piezoresistive sensor, a piezoresistive capacitive sensor, a photodiode-based sensor, an ultrasonic sensor, a pressure sensor, an organic thin film transistor sensor, an optical sensor, a 3D scanner, a ruler, a caliper, a micrometer, a feeler gauge or a combination sensor comprising at least one of these sensors.

32. The measurement system (200) of claim 31, wherein the sensor is an array sensor.

33. The measuring system (200) according to claim 31, wherein the sensor unit (210) comprises an image acquisition device and the analyzing unit (220) is adapted for image analysis.

34. The measuring system (200) according to any one of claims 31 to 33, wherein the analyzing unit (220) is adapted to determine the degree of asymmetric change of the determined dimensional change of the measuring nut (100) by means of a mathematical curve fitting method.

35. The measurement system (200) according to claim 34, wherein the mathematical curve fitting method is the least squares method, the moment method or the maximum likelihood method.

36. The measuring system (200) according to claim 34, wherein the analyzing unit (220) is adapted to compare the extent of the asymmetry change with a preselectable threshold level.

37. The measurement system (200) of claim 34, wherein the measurement system (200) further comprises a warning system (230), the warning system (230) being adapted to send a warning.

38. The measurement system (200) of claim 37, wherein the warning is an auditory, visual and / or tactile warning.

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