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) adapted to be attached to an object, such as a bolt or screw, and a non-contact portion (104), the contact portion (102) and the non-contact portion (104) being positioned coaxially but axially offset with respect to one another. The method includes: attaching at least a portion of the contact portion to the object, the non-contact portion being not in direct contact with the object; exposing the object to an external load, thereby causing a dimensional change in the contact portion of the measurement nut; and determining a dimensional change of the measurement nut by measurement at the non-contact portion. The invention further relates to a measuring nut (100) and a measuring system (200) comprising a measuring 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] In conventional techniques for measuring tension, tension can be measured at the object itself. Thereby, a sensor is 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 may, for example, be a strain gauge. However, strain gauges are rather expensive and not easy to use in practical locations. Thus, they are not particularly suitable for conventional settings. They will need to be calibrated before the measurement in order to obtain reliable measurements. Strain gauges are typically glued to the object to be measured. However, the glue is usually not stable over time, and thus there will be a need for recalibration in order 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 the prestress. The nut is of standard design and the nut itself constitutes the sensor body, since in the outer peripheral surface of the nut. At least one recess is machined, in which recess a sensor is placed, which is suitable for sensing mechanical stress in the nut and for providing 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 affects its mechanical properties in a negative way.

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

[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 a recess like 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 invention, a method of 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 external loads, thereby causing a change in the dimensions 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 the measuring nut is exposed, which in turn is the result of the external load applied to the object. In other words: when the object is exposed to an external load, the external load induces a tension in the object and thereby also in the measuring nut via the contact portion in direct contact with the object. Therefore, the external load will cause a dimensional change of the contact portion and also of the non-contact portion. By measuring at the non-contact portion of the measuring nut instead of at the contact portion of the measuring nut, 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 in which the measuring nut is in full contact with the object (as in the device of US2006 / 0225511A1) or is measured at the object itself, the dimensional change of the measuring nut can be measured with higher accuracy and thereby the tension of the object can be measured indirectly.

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

[0017] The object is typically a mechanical component, such as a bolt or a screw or any other mechanical component, which 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 structure carrying the load. Thus, the object may be part of another larger entity, such as equipment, machine or vehicle.

[0018] The external load applied to the object may be a tensile force, a compressive force, a shear force, a torsion force, a bending force, a gravitational force, a force caused by a temperature difference, or any combination of such forces. Such forces are known to induce tension in the object, which can be determined with the method for determining the dimensional change of the measuring nut, with the measuring nut, and with 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 around the inner hole. In that case, the internal thread of the contact portion is typically intended to be attached to the corresponding external thread of the object to be measured. Alternatively or as a supplement, 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, that is, when it is in direct contact with the object, for example via a 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] The measurement may be performed at the top surface of the non-contact portion. At least a portion of this surface faces in the axial direction of the measuring nut. Measurement at the top surface may be beneficial when the space around the measuring nut is limited so that it would be difficult to access one or more side surfaces. If measured at the top surface, a single measurement may be sufficient, the measurement preferably being performed at or around the length axis of the measuring nut. The term top surface refers to a surface positioned at the top of the non-contact surface. Depending on how the measuring nut is attached to the object, the top surface may face in any direction, for example downwards.

[0021] When the measuring nut is a capped nut comprising a capping portion included in the non-contacting portion of the measuring nut, the measurement at the top surface may be advantageous. In that case, the measurement is typically performed at the top surface of the capping portion, preferably at or around the length axis of the measuring nut. If capped, the measuring nut is preferably positioned such that the non-contacting portion is axially offset from the object.

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

[0023] Measurements may be performed at each side surface of the measuring nut. If measurements are not performed at each side surface, it is typically beneficial to select the side surfaces to be measured so that they are not adjacent to each other and so that they are evenly distributed around the periphery of the measuring nut. A typical nut comprises six side surfaces, and so does a typical measuring nut. Thus, measurements may be performed, for example, at all six side surfaces, at three side surfaces spaced 120 degrees apart, or at two opposite side surfaces spaced 180 degrees apart. If measurements are taken at the side surfaces, it may be beneficial to measure at more than one side surface in order to capture possible asymmetric dimensional changes of the measuring nut.

[0024] The contact portion of the measuring nut may comprise a threaded first portion and a threaded second portion, the non-contact portion being positioned between the threaded first portion of the contact portion and the threaded second portion, wherein the measurement is performed at the non-contact portion between the threaded first portion of the contact portion and the threaded second portion. Preferably, the measurement is performed midway between the threaded first portion of the contact portion and the threaded second portion. This way of using the method is beneficial when the object is a rod, such as a screw, wherein the side of the measuring nut is accessible from the side of the rod. In this case, the measuring nut will follow the axial movement of the rod when the rod is exposed to an external load.

[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 made under different tensioning conditions 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 supplement to using a measuring recess when performing a measurement, the measurement can be performed in a through-going measuring hole provided in the non-contact portion. Preferably, the measuring hole is provided at the top surface and / or at least one side surface of the non-contact portion. The measuring hole can typically have a circular cross-section.

[0029] The measuring recess and / or the measuring hole will weaken the mechanical strength of the non-contact part, which helps to amplify the dimensional change of the measuring nut when measuring at the non-contact part. In addition, the measuring recess and / or the measuring hole can provide a suitable docking site for the sensor unit. Thereby, docking can be easily performed in a similar manner and with high accuracy for each measurement.

[0030] The size change can be determined by means of 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 piezocalytic 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. The sensor can be of the type commonly used for fingerprint detection, for example in a smartphone. The sensor can be an array sensor, which can include a plurality of sensors as mentioned herein. The sensor unit forms part of a measuring 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 may be adapted to dock with the measuring nut. In particular, the sensor unit may be adapted to dock with the measuring recess and / or measuring hole disclosed herein. Thus, the sensor unit may have sufficient size and shape to fit neatly within the measuring recess or measuring hole.

[0032] The measurement can be performed with the aid of a pattern included in the non-contact portion or included in the object. The pattern can include a circle, a straight line or a dot pattern. The pattern can be positioned in a measuring recess of the measuring nut. In that case, the measuring recess will help protect the pattern from unintentional damage.

[0033] The pattern may be positioned on the surface of the non-contact part or object. The pattern may also be protected, for example, by a protective surface coating (e.g., paint) or a protective covering. In any case, the pattern is determinable from the outside of the non-contact part or object. Thus, the sensor unit is able to determine the pattern, for example, by a protective coating or covering, which may, for example, be 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 a projection of the pattern (if not 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 intrinsic or provided on at least a part 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 the manufacture of the component.

[0037] If provided, a pattern may be provided for the purpose of performing the measurement. Providing a pattern may include applying one or more patterns to the non-contact portion or object. The pattern may be applied to the non-contact portion or object, for example, by printing, laser gravure, mechanical gravure, etching, drilling, milling, turning, sputtering or electrical discharge machining. The pattern may be an applied surface structure, similar to knurling. Alternatively, the pattern may be provided on a separate film 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 other than determining tension, but in any case, 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 mentioned 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 interfacing 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 a non-contact portion being in an untensioned state. 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. The grooves may be centered around the length axis if measured at the top surface. Multiple concentric circular grooves may be used.

[0042] The pattern can be represented as different material properties, for example, the pattern elements are areas 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. The reference can then be made 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 known applied direction has been applied to the measuring nut.

[0044] The pattern may comprise a code which may be unique for the measuring nut where the pattern is located, thereby providing a unique identification for the measuring nut. The code may be readable by means of an encryption key, for example provided as an algorithm in an analysis unit comprised in a measuring system, which also comprises the measuring nut and the sensor unit. If the identification of the measuring nut is known, further information of the measuring nut, for example about the tension characteristics, may be linked to this specific measuring nut via the identification. The further information may be stored in a database, for example in the cloud.

[0045] The pattern may be formed with known distances between pattern elements in the untensioned state of the measuring nut, which distances may be utilized as references for data analysis. It is then not necessary to store reference data for the purpose of determining dimensional changes. However, the storage of reference data may be of interest anyway, as it may show 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 using 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] Also alternatively or additionally, the reference information may be included in the pattern itself, for example as information points included in the pattern, for example with information about the position of pattern elements or the distance 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 the reaction of the non-contact portion to multiple tensions.

[0048] The pattern may be positioned in one or more of the measurement recesses described herein. Thus, the risk of accidentally damaging the pattern is reduced 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 if the object is subject to high loads or even excessive loads, such as torsion. It can further be determined whether the load is central 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, most preferably 3-5 slots, the at least one slot being used to increase the dimensional change of the non-contact portion caused by the contact portion. Thus, when measuring, the slot (slots) may be used to amplify the dimensional change occurring in the contact portion of the measuring nut, thereby improving the accuracy of the measurement.

[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 of the measuring nut is preferably the untensioned state. This measurement can be performed by the manufacturer of the measuring nut. The reference measurement only has 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, for example an applied number, a barcode or a QR code.

[0058] As an alternative or in addition, 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 (e.g. a bolt) to which the measuring nut is attached. 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 reasons 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 angling of the joint faces. 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 large local tensions may affect 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 a mathematical curve fitting method (such as the least squares method, the method of moments or the maximum likelihood method). 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 used 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 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, 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] - When the determined degree of asymmetry change exceeds a preselectable threshold level, sending a warning, for example an audible, visual and / or tactile warning.

[0069] According to a second aspect of the invention, there is provided a measuring nut comprising 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 are positioned coaxially but axially offset relative to each other. The measuring nut is provided with a measuring zone at the non-contact portion, the measuring zone being adapted to determine a change in the dimension of the measuring nut attached to the object.

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

[0071] When the contact portion is attached to the object, i.e. in direct contact with the object, the non-contact portion remains without any direct contact with the object. Thus, the non-contact portion can change its dimensions independently of the object. The non-contact portion can, for example, 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 part of the object.

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

[0073] The contact portion of the measuring nut may 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 measuring zone is positioned between the threaded first portion and the threaded second portion of the contact portion. Preferably, the measuring 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 may be beneficial when the object is a rod, for which the side portion is easily 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, the movement being measured as a dimensional change at the measuring zone.

[0074] The non-contact portion may include at least one rod, such as two or three rods, spanning between the threaded first portion and the threaded second portion. There may further be at least one side portion included in the non-contact portion, such as two or three sides having corresponding side surfaces. The at least one side portion may be separated, for example, in the middle by a slot of the kind described herein. The measurement area may be positioned in the side portion, such as so that it is separated by a slot.

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

[0076] The non-contact portion of the measuring nut according to the invention may be unthreaded, since it is not intended to come into direct contact with an object. However, in some embodiments, it is easier to provide both the contact portion and the non-contact portion with threads during manufacture of the measuring nut, although the threads of the non-contact portion are not intended to be used.

[0077] The non-contact portion may include at least one slot extending in the axial direction, preferably 1-10 slots, more preferably 2-6 slots, most preferably 3-5 slots. The slot (slots) may be used to amplify the dimensional change occurring in the contact portion of the measuring nut, thereby improving the accuracy of the measurement.

[0078] The at least one slot may extend in the axial direction by 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. It may extend over the entire length of the non-contact portion.

[0079] The at least one slot may extend in radial direction by at least 80%, preferably at least 90%, more preferably at least 95%, most preferably 100% of the radial extension of the non-contact portion. Thus, the non-contact portion may be divided into sub-portions by the slots. If the non-contact portion comprises a central 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 suitable 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 may include a pattern, which is inherent or applied, such as a groove. The pattern may include a circle, a straight line or a dot pattern. The pattern may be positioned in the measurement recess. For further details and advantages of the pattern, see the description of the method.

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

[0085] According to a third aspect of the invention, there is provided a measuring system comprising: a measuring nut as described herein; a sensor unit adapted to interface with the measuring nut to determine a change in the size of the non-contact portion of the measuring nut by measuring at or by means of the measuring region; and an analysis unit adapted to determine the change in the size of the measuring nut from the determined change in the size 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 in this article. Therefore, the details described in this article for the method can also be applied to the measurement system. In addition, the advantages described in this article about 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 piezocalytic 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 gap gauge or a combination sensor including at least one of these sensors. The sensor may be of the type commonly used for fingerprint detection, for example in a smartphone. The sensor may be an array sensor, which may include a plurality of sensors as mentioned herein. Since 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 wherein the analysis unit is 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 torsion or even excessive torsion. It may be determined whether the load is centered or eccentric.

[0089] In a measuring system where the measuring nut includes a through-going measuring hole, the sensor unit may be adapted to interface with the through-going measuring hole. Thus, the sensor unit may have a sufficient size and shape to fit neatly within the measuring hole. This is suitable for making measurements using a pattern positioned at 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, such as 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 audible, 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 installed correctly. Therefore, if the determined degree of asymmetry change exceeds a threshold level, an operator performing the bolt joint application may be warned of misalignment by the measurement system (e.g., by a warning system included in the measurement system). The operator may 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 1a to 1e A measuring nut according to a first embodiment of the 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] Figure 5a to Figure 5d A measuring nut according to a second embodiment of the invention is shown.

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

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

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

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

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

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

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

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

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

[0110] Fig.10aThe screw is shown with a measuring zone.

[0111] Fig.10b The flange is shown with the measuring area provided.

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

[0113] The present invention will be illustrated by examples below. However, it should be appreciated that each embodiment is included to explain the principles of the present invention, rather than to limit the scope of the present invention as defined by the appended claims. Details from two or more of the embodiments may be combined with each other.

[0114] Figures 1a to 1e A measuring nut 100 according to a first embodiment of the invention is shown. Figure 1a Showing a perspective view, Figure 1b Showing a top view, Figure 1c Showing a side view, Figure 1d Shown along Figure 1b The cross-sectional view is taken along line AA in FIG. Figure 1e Shown along Figure 1c A cross-sectional view taken along line BB in FIG.

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

[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 coaxially located, i.e. about the same length axis A, but axially offset relative to each other, wherein the non-contact portion 104 is located on top of the contact portion 102 in the perspective view shown. The measuring nut 100 is provided with a measuring area 106 at a top surface 108 of the non-contact portion 104. The measuring area 106, which in the embodiment shown comprises a measuring recess 110, is suitable for determining a change in the size of the measuring nut 100 when it is attached to an object.

[0117] The dimensional change of the measuring nut 100 is caused by the tension to which the measuring nut 100 is exposed, which in turn is a result of the external load applied to the object. In other words: when the object is exposed to an external load, the external load induces a tension in the object and thereby also in the measuring nut 100 via the contact portion 102 in direct contact with the object. Therefore, the external load will cause a dimensional change of the contact portion 102 and also of the non-contact portion 104. By measuring at the non-contact portion 104 of the measuring nut 100 instead of at the contact portion 102 of the measuring nut 100, 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 the prior art solutions of measuring at the contact portion of the measuring nut or at the object itself, the dimensional change of the measuring nut 100 can be measured with higher accuracy and thereby the tension of the object can be indirectly measured with higher accuracy.

[0118] The measuring nut 100 is formed as Figure 2 A portion of the 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 analyzing 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 piezocalytic 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 a type commonly used for fingerprint detection, such as in a smartphone. The sensor may be an array sensor, which may include a plurality of sensors mentioned herein.

[0120] like Figure 1d As best seen in the figure, the contact portion 102 is internally threaded. The internal thread 112 is intended to be attached to a corresponding external thread of the object to be measured. In the embodiment shown, the non-contact portion 104 is non-threaded. It is not intended to come into direct contact with the object. However, sometimes it is easier to provide threads for both the contact portion 102 and the non-contact portion 104 during the 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 first embodiment shown, the measuring nut 100 is a cover nut including a cover portion 114 which forms a cover for the non-contact portion 104. Figure 1d The measuring area 106 with its measuring recess 110 is positioned in the cover part 114 .

[0122] The measuring nut 100 is provided with four slots 116a-116d evenly distributed around the periphery of the non-contact portion 104. In the illustrated embodiment, the slots 116a-116d extend axially through the entire axial length of the non-contact portion 104, see Figure 1a and Figure 1c , and have an open end facing upward. The slots 116a-116d extend radially through the non-contact portion 104, see Figure 1a , Figure 1b and Figure 1e In the cover portion 114, the slots 116a-116d 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-116d extend through the entire wall thickness. Thus, the slots 116a-116d divide the non-contact portion 104 into four sub-portions 120a-120d. The slots 116a-116d are used to magnify the dimensional changes of the contact portion 102 when measured at the measurement area 106.

[0123] The measurement zone 106 to which the sensor unit 210 is intended to be docked is provided with a pattern in the form of circular grooves 122, such as Figure 1a and Figure 1b The circular recess 122 is centered about the length axis A. It is located in the measuring recess 110.

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

[0125] 310: attaching at least a portion of the contact portion 102 to an object, wherein the non-contact portion 104 is not in direct contact with the object,

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

[0127] 330 : Determine the dimensional change of the measuring nut 100 by measuring at the non-contact portion 104 .

[0128] This measurement is available Figure 2 The measurement system 200 shown in FIG. 1 is performed. When using a method similar to Figures 1a to 1eWhen 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 Figure 5a to Figure 5d , Figures 6a to 6c , Figure 7 as well as Figure 8a to Figure 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. The array sensor is typically two-dimensional with an analysis unit 220 suitable for image analysis.

[0130] The 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 dimension of the measuring nut 100 in step 330 .

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

[0134] As an alternative or in addition, 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, such as Figures 1a to 1e 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 1a to 1e The circular groove 122 of the measuring nut 100 is formed. Figure 4b An exemplary representation of the measured data is shown. The solid line shows the measurement result of the circular groove 122 in the untensioned state (i.e. 0 Nm). The scale is given in pixel units of the image acquisition device, where 1 pixel is 0.05 mm. Therefore, for the circular groove 122 of the untensioned measuring nut 100 of the exemplary embodiment, the radius is about 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 due to the contact of the thread 112 with the object stretching the contact portion 102, as shown by Figure 4b, which represents the applied torque of 500 Nm causing tension to the object and thus to the measuring nut 100. By comparing the dotted 500 Nm measurement result with the solid line of the 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 of the object can be deduced from the measured dimensional change.

[0138] Figure 5a to Figure 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] The measuring nut 500 is provided with three slots 516a, 516b, 516c extending through the entire axial length of the non-contact portion 504. They also extend through the entire wall thickness of the non-contact portion 504. Therefore, they divide the non-contact portion 504 into three sub-portions 520a-520c. In addition, the slots 516a-516c extend through the respective measuring areas 506a-506c, dividing them into two halves and dividing the circular groove 522 into two semicircles.

[0142] Figures 6a to 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 includes a first threaded portion 602a and a second threaded portion 602b, and the non-contact portion 604 is positioned between the first threaded portion 602a and the second threaded portion 602b of the contact portion 602. Figure 6a 602). The axial length of the contact portion 602 is the sum of the axial lengths of the first threaded portion 602a and the second threaded portion 602b. The first threaded portion 602a and the second threaded portion 602b are connected to each other via the non-contact portion 604. The non-contact portion 604 includes two rods 624a, 624b spanning between the first threaded portion 602a and the second threaded portion 602b. The non-contact portion 604 further includes two side portions 626a, 626b having corresponding side surfaces 608a, 608b. The side portions 626a-626b are separated in the middle by corresponding slots 616a, 616b. Therefore, the slots 616a-616b are open at both ends.

[0144] There are two measurement areas 606a, 606b, each comprising a measurement recess 610a, 610b. They are positioned in the side 626a, 626b between the threaded first portion 602a and the threaded second portion 602b, and in the embodiment shown, in the middle between the threaded first portion 602a and the threaded second portion 602b. The positioning at the side 626a, 626b makes the measurement areas 606a-606b accessible from the side of the rod. When the rod is exposed to external loads, the measuring nut 600 will follow the axial movement of the rod, which movement can be measured as a change in size at the measurement areas 606a, 606b. The measurement areas 606a, 606b may include a pattern not shown, for example similar to Figures 1a to 1e and Figure 5a to Figure 5d The circular grooves 122, 522 of the embodiment.

[0145] Figure 7 The fourth embodiment of the measuring nut 700 shown in FIG. Figure 5a to Figure 5dThe second embodiment shown has many of the same features as the second embodiment. It includes a threaded contact portion 702 and a non-contact portion 704. Instead of having a measurement zone formed by measurement recesses 510a-510c as in the second embodiment, the non-contact portion 704 is provided with a measurement zone formed by three through-going measurement holes 724a-724c. These are used as docking sites for the sensor unit 210 of the measurement system 200. When the sensor unit 210 docks in one of the measurement holes 724a-724c, the sensor unit 210 follows the displacement of the non-contact portion 704, which in turn is caused by the object being tensioned. Since the holes 724a-724c are through-going, the sensor unit 210 can use a pattern provided on the object in order to determine the change in the size of the measurement nut 700. In the case where the object includes an external thread, the pattern on the object can be a thread, or the object can be intentionally provided with a pattern detectable through the holes 724a-724c, such as a QR code, a bar code or a 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. 1 , 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] Figure 8a to Figure 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] The measuring nut 800 includes a threaded contact portion 802 and a non-threaded non-contact portion 804. The non-contact portion 804 includes a first portion 804a and a second portion 804b, and the contact portion 802 is positioned between the first portion 804a and the second portion 804b of the non-contact portion 804. The axial length of the non-contact portion 804 is the sum of the axial lengths of the first portion 804a and the second portion 804b.

[0148] The non-contact portion 804 is provided with a measurement zone in the form of a through-going measurement hole 824a-824f positioned at the side surface. Alternatively, a measurement recess may be provided, for example, a measurement recess similar to that described for the first to third embodiments. 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 on the positioning at the side surface, see the comments for the second, third and fourth embodiments. For comments on the measurement holes 824a-824f, see the comments 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 1a to 1e The circular groove of the measuring nut 100 is also Figure 4a Shown in. Figure 9a and Figure 9b The solid line measurement results of the circular groove 122 respectively show the measurement results in the untensioned state, that is, at 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 is intended to cooperate with an object, such as, for example, a bolt 124 or a screw, in Figure 9c to Figure 9f 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, which represents an applied torque of 500 Nm, which causes tension on the object and thus on 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 the dimensional change of the measuring nut 100 can be determined thereby. Thereafter, the tension of 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 1a to 1e .

[0151] Figure 9a A measurement example is shown for which the 0 Nm and 500 Nm measurement results are substantially symmetrical, i.e. the 500 Nm measurement result has the same overall shape but a slightly smaller radius, showing an ideal measurement situation. This is the desired measurement situation, as Figure 9c to Figure 9f As shown in Fig.9c A side view is shown, and Figure 9d Shown along Fig.9c DD. Figures 1a to 1e In contrast, the measuring nut 100 is positioned upside down so that the top surface 108 of the non-contact portion 104 faces 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. Therefore, the bolt 124 is positioned in a straight and aligned manner relative to the measuring nut 100. Therefore, the 500Nm measurement is located inside the 0Nm 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 Figure 9e to Figure 9f As shown in Fig.9e A side view is shown, and Figure 9f Shown along Fig.9e FF. This may be due to dirt and / or paint on the surface. Other causes may be errors that occurred during the manufacture and / or installation of the bolt 124' or the washer 126'. This misalignment of bolt joint applications is sometimes referred to as angularity of the joint faces. As a consequence, the bolt 124' and the measuring nut 100 will be loaded asymmetrically, generating large local tensions. Finally, this problem may be detrimental to the bolt joint application, since large local tensions may affect fatigue strength in a negative way.

[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 than in 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 in order to detect the degree of misalignment, also known as angulation of the joint faces, when it 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 substantially 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 , 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 results determined in the tensioned state can be compared with the untensioned measurement results or the nominal radius of the circular groove 122. Thus, the difference between the two measurement results can be determined using mathematical curve fitting methods (such as the least squares method, the moment method or the maximum likelihood method). Figure 9a and Figure 9bTo measure the results, 960 radii were determined equidistantly around the perimeter of the circular groove 122 and the standard deviation was used to quantify the difference from the 0 Nm measurement, which was first determined and stored for comparison.

[0156] If the degree of asymmetry change is high, this is a sign that the bolt joint application was not installed correctly. 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 acceptable degree of asymmetry change. If the determined degree of asymmetry change exceeds the threshold level, the operator performing the bolt joint application can be warned of misalignment by the measuring system 200 (e.g., by the warning system 230 included in the measuring system 200), see Figure 2 The operator can then loosen the bolted joint application and make some adjustments, such as adjusting the washers, before re-bolting the joint.

[0157] Therefore, if the interest is in determining misalignment or joint face angulation, the method 300 described herein (see Figure 3 ) may further include the optional steps of:

[0158] 340: Determine the degree of asymmetric change of the determined dimensional change.

[0159] Additionally, the method 300 may include the following steps:

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

[0161] 360: If the determined degree of asymmetry change exceeds a preselectable threshold level, a warning is sent.

[0162] The warning may be audible, visual and / or tactile. It may be sent by a warning system 230 included in the measurement system 200, see Figure 2 , the warning system 230 is for example positioned as a single integral unit together with the analysis unit 220. For example there may be a buzzer, a light may change color and / or flash, or the tool for tightening the measuring nut 100 may vibrate. Thus, the warning system 230 may include one or more LEDs and / or a speaker.

[0163] Even though the measurement of misalignment or joint face angulation has been illustrated above by means of an illustration in the form of circular grooves 122, it would be possible to use other patterns, for example similar to those described herein. The measuring nut may further be of any type described herein.

[0164] Furthermore, corresponding measurements can be made on other kinds of connections, such as screw connections, in order to detect misalignment or angulation of the joint faces. The measurement of misalignment or angulation of the joint faces can be performed by means of a measuring nut 100, as shown, but can also be performed at, for example, a bolt, a screw, a threaded rod, a washer or a spacer.

[0165] Furthermore, it may be relevant to measure the degree of asymmetric changes for any element in which dimensional changes may occur, for example due to external loads. Examples of such elements are bolts, screws, threaded rods 1002 (see Fig.10a ), gasket, spacer or flange 1004 (see Fig.10b ). The external load applied to the element may be a tensile force, a pressing force, a pressure force, a shear force, a torsion force, a bending force, a gravity force, a force caused by a temperature difference, or any combination of such forces. Such forces are known to induce 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 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 (e.g. 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 intentionally caused by the aforementioned optional steps included in 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 determined degree of asymmetry change exceeds a preselectable preselected threshold level, a warning is sent.

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

[0177] - determining a pattern comprised 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 asymmetric change of an element may further comprise:

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

[0181] - Reference measurements are used when determining dimensional changes of 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 an element, as they are applicable.

[0183] Further modifications of the present invention within the scope of the appended claims are feasible. Thus, the present invention should not be considered to be limited by the embodiments and drawings described herein. On the contrary, 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, 500, 600, 700, 800), the measuring nut (100, 500, 600, 700, 800) comprising a contact portion (102, 502, 602, 702, 802) and a non-contact portion (104, 504, 604, 704, 804), the contact portion (102, 502, 602, 702, 802) being suitable for attachment to an object, such as a bolt or a screw, the contact portion (102, 502, 602, 702, 802) and the non-contact portion (104, 504, 604, 704, 804) being coaxially but axially offset relative to each other, The method comprises: - attaching (310) at least a portion of the contact portion (102, 502, 602, 702, 802) to the object, the non-contact portion (104, 504, 604, 704, 804) 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, 502, 602, 702, 802), and - determining the dimensional change (330) of the measuring nut (100, 500, 600, 700, 800) by measuring at the non-contact portion (104, 504, 604, 704, 804).

2. The method according to claim 1, wherein the measuring is performed at a top surface (108) of the non-contact portion (104).

3. The method according to claim 1 or 2, wherein the measurement is performed at at least one side surface (508a, 508c, 508e; 608a, 608b) of the non-contact portion (504, 604, 704, 804), for example at two or three side surfaces.

4. According to the method of claim 3, the contact portion of the measuring nut (600) includes a threaded first portion (602a) and a threaded second portion (602b), and the non-contact portion (604) is positioned between the threaded first portion (602a) and the threaded second portion (602b) of the contact portion, wherein the measurement is performed at the non-contact portion (604) between the threaded first portion (602a) and the threaded second portion (602b), and preferably the measurement is performed in the middle between the threaded first portion (602a) and the threaded second portion (602b).

5. A method according to any one of the preceding claims, wherein the measurement is performed in a measuring recess (110, 510a-510c, 610a-610b) arranged in the non-contact portion (104, 504, 604), preferably in a measuring recess arranged at the top surface (108) of the non-contact portion (104) and / or at least one side surface (508a-508c; 608a, 608b) of the non-contact portion (504, 604).

6. A method according to any one of the preceding claims, wherein the measurement is performed in a through measuring hole (724a-724c; 824a-824f) arranged in the non-contact portion (704, 804), preferably in a measuring hole (724a-724c; 824a-824f) arranged at the top surface and / or at least one side surface of the non-contact portion.

7. A method according to any of the preceding claims, wherein the dimensional change is determined with the aid 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 piezocappic 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 gap gauge or a combination sensor comprising at least one of these sensors, the sensor being for example an array sensor.

8. Method according to any of the preceding claims, wherein the measuring is performed with the aid of a pattern comprised in the non-contact portion (104, 504, 604) or in the object, the pattern being inherent or provided, such as a groove (122, 522).

9. The method according to claim 8, wherein the method comprises: - determining the pattern by means of an array sensor, such as an image acquisition device, - Using image analysis to derive dimensional information from the pattern.

10. The method according to any one of the preceding claims, wherein the non-contact portion (104, 504, 604) of the measuring nut (100, 500, 600) comprises at least one slot (116a-116d; 516a-516c; 616a-616b), preferably 1-10 slots, more preferably 2-6 slots, most preferably 3-5 slots, extending at least partially in the axial direction (A) of the measuring nut (100, 500, 600), the at least one slot (116a-116d; 516a-516c; 616a-616b) being used to increase the dimensional change of the non-contact portion (104, 504, 604) caused by the contact portion (102, 502, 602).

11. The method according to any one of the preceding claims, wherein the method further comprises: - performing a reference measurement (305) at the non-contact portion (104, 504, 604, 704) under a known tension of the measuring nut (100, 500, 600, 700), and - using said reference measurement when determining said dimensional change (330) of said measuring nut (100, 500, 600, 700).

12. The method according to any one of the preceding claims, wherein the method further comprises: The degree of asymmetric change of the determined dimensional change of the measuring nut (100) is determined (340), for example by means of a mathematical curve fitting method, such as the method of least squares, the method of moments or the method of maximum likelihood.

13. The method according to claim 12, wherein the method further comprises: - comparing the determined degree of asymmetry change with a preselectable threshold level (350), And optional steps: - sending (360) a warning, such as an audible, visual and / or tactile warning, when the determined degree of asymmetry change exceeds said preselectable threshold level.

14. Measuring nut (100, 500, 600, 700, 800), including: - a contact portion (102, 502, 602, 702, 802) suitable for attachment to an object, such as a bolt or a screw, and - Non-contact part (104, 504, 604, 704, 804), The contact portion (102, 502, 602, 702, 802) and the non-contact portion (104, 504, 604, 704, 804) are coaxially positioned relative to each other but axially offset, It is characterized in that The measuring nut (100, 500, 600, 700, 800) is provided with a measuring area (106; 506a-506c; 606a, 606b; 724a-724c; 824a-824f) at the non-contact portion (104, 504, 604, 704, 804), and the measuring area (106; 506a-506c; 606a, 606b; 724a-724c; 824a-824f) is suitable for determining the dimensional change of the measuring nut (100, 500, 600, 700, 800) attached to the object.

15. The measuring nut (100) according to claim 14, wherein the measuring area (106) is positioned at a top surface (108) of the non-contact portion (104).

16. The measuring nut (500, 600, 700, 800) according to claim 14 or 15, wherein the measuring area (506a-506c; 606a-606b; 724a-724c; 824a-824f) is positioned at at least one side surface (508a-508c; 608a-608b) of the non-contact portion (104, 504, 604, 704, 804), for example at two or three side surfaces.

17. The measuring nut (600) according to claim 16, wherein the contact portion (602) of the measuring nut (600) comprises a first threaded portion (602a) and a second threaded portion (602b), the non-contact portion (604) is positioned between the first threaded portion (602a) and the second threaded portion (602b), and preferably, the measuring area (606a, 606b) is positioned in the middle between the first threaded portion (602a) and the second threaded portion (602b).

18. The measuring nut (800) according to any one of claims 14 to 16, wherein the non-contact portion (804) of the measuring nut (800) comprises a first portion (804a) and a second portion (804b), and the contact portion (802) is positioned between the first portion (804a) and the second portion (804b) of the non-contact portion (804).

19. The measuring nut (100, 500, 600, 700, 800) according to any one of claims 14 to 18, wherein the non-contact portion (104, 504, 604, 704, 804) is non-threaded.

20. The measuring nut (100, 500, 600) according to any one of claims 14 to 19, wherein the non-contact portion (104, 504, 604) comprises at least one slot (116a-116d; 516a-516c; 616a-616b) extending in the axial direction (A) of the measuring nut (100, 500, 600), preferably 1 to 10 slots, more preferably 2 to 6 slots, most preferably 3 to 5 slots.

21. The measuring nut (100, 500, 600) according to claim 20, wherein the at least one slot (116a-116d; 516a-516c; 616a-616b) extends in the axial direction (A) of the measuring nut (100, 500, 600) by at least 40%, preferably at least 60%, more preferably at least 80%, and most preferably at least 95% of the axial length of the non-contact portion (104, 504, 604).

22. The measuring nut (100, 500, 600) according to claim 20 or 21, wherein the at least one slot (116a-116d; 516a-516c; 616a-616b) extends 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 range of the non-contact portion (104, 504, 604).

23. The measuring nut (100, 500, 600, 700, 800) according to any one of claims 14 to 22, wherein the non-contact portion (104, 504, 604, 704, 804) has an axial length in the range of 25%-3000% of the axial length of the contact portion (102, 502, 602, 702, 802), for example, in the range of 50%-1000% or 50%-500% or 50%-250% or 75%-125%.

24. The measuring nut (100, 500, 600, 700, 800) according to any one of claims 14 to 23, wherein the measuring area (106; 506a-506c; 606a, 606b) comprises a measuring recess (110; 510a-510c, 610a, 610b) and / or a through-going measuring hole (724a-724c; 824a-824f).

25. The measuring nut (100, 500, 600) according to any one of claims 14 to 24, wherein the measuring zone (106; 506a-506c; 606a, 606b) comprises a pattern, which is inherent or applied, such as grooves (122, 522).

26. The measuring nut (100, 500, 600) according to claim 25, wherein the pattern comprises circles (122, 522), straight lines or a dot pattern.

27. The measuring nut (100, 500, 600, 700, 800) according to any one of claims 14 to 26, wherein the measuring nut is provided with a unique identifier.

28. A measurement system (200), comprising: - A measuring nut (100, 500, 600, 700, 800) according to any one of claims 14 to 27, a sensor unit (210) adapted to interface with the measuring nut (100, 500, 600, 700, 800) to determine a change in the size of the non-contact portion (104, 504, 604, 704, 804) of the measuring nut (100, 500, 600, 700, 800) by measuring at or by means of the measuring region (106; 506a-506c; 606a, 606b; 724a-724c; 824a-824f), and An analyzing unit (220) adapted to determine a change in size of the measuring nut (100, 500, 600, 700, 800) from the determined change in size of the non-contact portion (104, 504, 604, 704, 804).

29. The measuring system (200) of claim 28, 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 piezocappic 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 gap gauge or a combination sensor comprising at least one of these sensors, the sensor being, for example, an array sensor.

30. The measuring system (200) according to claim 28 or 29, wherein the sensor unit (210) comprises an array sensor, such as an image acquisition device, and wherein the analyzing unit (220) is adapted for image analysis.

31. A measuring system (200) according to any one of claims 28-30, wherein the measuring nut (700) includes a through measuring hole (724a-724c; 824a-824f), and the sensor unit (210) is suitable for docking with the through measuring hole (724a-724c; 824a-824f).

32. A measuring system (200) according to any one of claims 28 to 31, wherein the analysis unit (220) is suitable for determining the degree of asymmetric change of the determined dimensional change of the measuring nut (100), for example by means of a mathematical curve fitting method, such as the least squares method, the moment method or the maximum likelihood method.

33. The measuring system (200) according to claim 32, wherein the analyzing unit (220) is adapted to compare the extent of the asymmetry change with a preselectable threshold level.

34. The measurement system (200) according to claim 33, further comprising a warning system (230), the warning system (230) being adapted to send a warning, such as an audible, visual and / or tactile warning.

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