WO2025177193A1

WO2025177193A1 - Monitoring system

Info

Publication number: WO2025177193A1
Application number: PCT/IB2025/051819
Authority: WO
Inventors: Michele POGGIPOLINI
Original assignee: Sens In SRL
Current assignee: Sens In SRL
Priority date: 2024-02-22
Filing date: 2025-02-20
Publication date: 2025-08-28
Anticipated expiration: 2026-08-22
Also published as: WO2025177191A1

Abstract

A monitoring system having a control system (2) and a fastener (3), in particular a screw or a stud; wherein the control system (2) has, in turn, one or more sensing elements (18, 18d); wherein each sensing element (18, 18d) can be selected within a group of sensing elements different in type from each other; wherein each sensing element (18, 18d) is applied to a transversal surface (n1, n2), in particular perpendicular, to the longitudinal axis (Zl) of the fastener (3).

Description

"MONITORING SYSTEM"

Cross-Reference to Related Applications

This Patent Application claims priority from Italian Patent Applications No . 102024000003790 f iled on February 22 , 2024 , and No . 102024000003784 filed on February 22 , 2024 , the entire disclosure of which is incorporated herein by reference .

Technical Field

The present invention relates to a monitoring system .

Advantageously, the present invention relates to a monitoring system comprising a fastener, in particular a threaded element such as a screw .

Background Art

There is known, for example from WO 2023281429 Al , a fastener comprising one or more sensors and configured to be able to guarantee , in addition to its function of fastening components of a mechanical apparatus to one another, also the function of dynamic generation of signals ( in particular electromagnetic signals ) based on the operating conditions , i . e . , the instantaneous conditions of use , of the fastener in combination with any physical phenomena that instantaneously af fect the fastener, and the function of exchanging these signals with the outside world .

A prior art solution of the type described above provides for creating a longitudinal housing in the fastener, for example a hole that extends along the shank of a screw . The presence of this housing reduces the strength, in particular the fatigue strength, of the fastener and is not suitable to be produced in : fasteners of small si ze , for example M6 type screws ; or fasteners subj ected to high external stress .

The obj ect of the present invention is to provide a monitoring system that does not interfere with the resistant section, for example the shank, of the fastener.

Summary

According to the present invention, there is provided a monitoring system, as cited in the appended claims.

Brief Description of the Drawings

For a better understanding of the present invention, some embodiments are now described purely by way of non-limiting example, with reference to the accompanying drawings, wherein:

Fig. 1 is a schematic and partially sectional view of a monitoring system according to the present invention;

Fig. 2 is a plan view of a detail of Fig. 1;

Fig. 3 is a perspective view of a detail of Fig. 1;

Fig. 4 is an exploded view of a detail of Fig. 1;

Fig. 5 illustrates a variant of a monitoring system according to the present invention;

Figs. 6A, 6B, 6C, 6D, 6E are schematic views of a detail of the monitoring system according to the present invention; and Fig. 7 illustrates a further variant of a monitoring system according to the present invention.

Preferred Embodiment of the Invention

In Fig. 1, the reference number 1 indicates as a whole a monitoring system according to the present invention.

The monitoring system 1 comprises a control system 2 and a fastener 3.

The term fastener 3 is meant as an element configured to connect two or more mechanical components of a mechanical apparatus to one another. A fastener 3 is configured to be subjected, during use, to high mechanical stress. For example, the fastener 3 is configured to clamp bodies subjected to high dynamic stress, i.e., vibrations, and/or thermal stress. Advantageously, the fastener 3 is made of a material with high mechanical strength. By way of non-limiting example, the fastener 3 is made of a metallic material, such as: steel alloys, titanium alloys or equivalent materials.

According to the schematic example illustrated in Fig. 1, the fastener 3 is a screw. Advantageously, the fastener 3 can be a screw of small size, for example a screw generally classified as M6.

According to the example illustrated, the screw 3 comprises a shank 4 having a longitudinal axis Zl. The shank 4 is substantially cylindrical in shape and has a thread 5. According to the example illustrated, the thread 5 is external, i.e., it is produced on a respective external portion of the shank 4. The screw 3 comprises a head 6, configured to interact, in use, with a tightening tool (of known type and not illustrated, such as spanners, Allen keys or the like) . The arrangement and the shape of the profile of the thread 5 are variable. The number and the mutual arrangement of any additional threads 5 are variable.

Without loss of generality, the fastener 3 can differ from what is illustrated. For example, the fastener can be a stud, or can be coupled to a nut to form a bolt. For example, according to the present invention, the following can be considered as fasteners: rivets, screws, studs or the like. Fig. 5 illustrates a variant in which the fastener 3' is a stud, as will be better illustrated hereunder (it must be noted that hereunder and in the figures, the elements in common between the fasteners 3 and 3' have the same numbers and are not repeated for the sake of brevity) .

According to the example illustrated in Fig. 2, the fastener 3, 3' has a recess 7 in the head 6. The recess 7 is produced only within the head 6. In other words, the recess 7 does not affect the shank 4. Advantageously, the recess 7 is shaped with reference to two axes, identified hereunder with horizontal axis X and vertical axis Y, of a plane n perpendicular to the longitudinal axis Zl.

Hereunder, the system of axes XYZ1 and the plane n are taken as reference .

In particular, the recess 7 has a central portion 8 that is centred on the longitudinal axis Zl and two wings 9 opposite each other in relation to the central portion 8 (Fig. 2) . The wings 9 are aligned along the horizontal axis X. The shape and the size of the recess 7 are variable. Advantageously, the recess 7 is configured so as to allow the insertion and housing of objects, in particular thin bodies such as circuit boards, only if they have a given shape and orientation.

The control system 2 comprises, in turn, an electronic unit 10, at least partially flexible. Advantageously, the electronic unit 10 is a rigid-flexible printed circuit board, generally known as rigid-flex PCB .

The control system 2 further comprises a cap 11 that is configured to be fixed, in use, to the head 6 of the screw 3.

The control system 2 further comprises a connector 12 configured also to fix, at least partially, the electronic unit 10 within the cap 11.

According to the example illustrated in Figs. 1 and 3, the control system 2 further comprises a frame 14 to constrain the electronic unit 10 within the cap 11. According to the variant illustrated in Fig. 5, the control system 2 has no frame, as will be better illustrated hereunder.

Advantageously, the electronic unit 10 comprises a plurality of rigid parts 15 and a plurality of flexible parts 16 . Each rigid part 15 is a circuit board printed with conventional lithographic technologies or other technologies , such as additively manufactured electronics . Each flexible part 16 is a printed circuit board and electrically connects several rigid parts 15 to one another . According to the example illustrated, each flexible part 16 is a thin and elongated body having two ends "e" . Each end "e" is electrically connected to a respective rigid part 15 .

The number, shape and si ze of both the rigid parts 15 and the flexible parts 16 are variable .

According to the example illustrated, the electronic unit 10 comprises three rigid parts 15 , identi fied hereunder with : rigid measuring part 151 , rigid processing part 1511 , and rigid connection part 15I I I . It is speci fied that the distinction between the rigid parts 151 , 1511 and 15I I I is provided purely for explanatory purposes . In particular, the functions described hereunder can be distributed and performed by means of a di f ferent number and configuration of rigid parts 15 and/or flexible parts 16 .

According to the example illustrated, the electronic unit 10 further comprises a flexible part 161 , which is interposed between the rigid parts 151 and 1511 , and a flexible part 1611 , which is interposed between the rigid parts 1511 and 15I I I .

Advantageously, the electronic unit 10 is divided into a measuring portion PM, a processing portion PE and a connection portion PC . Each portion PM, PE , PC of the electronic unit 10 can comprise a rigid part 15 and/or a flexible part 16 .

In the example of Fig . 1 the measuring portion PM comprises a rigid measuring part 151 . In the variant illustrated in Fig . 7 , the measuring portion PM comprises both a rigid measuring part 151 and a flexible part 161 and/or a sensing element 18. According to a variant, not illustrated, the measuring portion PM comprises only a flexible part 16 and/or a sensing element 18.

In particular, the measuring portion PM comprises, in turn, one or more sensing elements 18. Advantageously, each sensing element 18 is miniaturised. Each sensing element 18 can be: a component integrated in the rigid measuring part 151 and/or in the flexible part 161; or can be a separate sensing element 18, connected to the rigid measuring part 151 and/or to the flexible part 161.

Each sensing element 18 can be selected within a group of sensing elements 18 different from each other. For example, the sensing elements 18 can be of: deformation, acceleration, temperature, pressure, tension, humidity, inclination, thermal flow, gas analysis and measuring solutions of other physical or equivalent quantities. Each sensing element 18 can be selected within a group of sensing elements 18 different in type from each other. Each sensing element 18 is configured to emit a signal depending on the operating conditions, i.e., the instantaneous conditions of use of the fastener 3 in combination with any physical phenomena that instantaneously affect the fastener 3 itself.

In particular, each sensing element 18 has its own reference system, which has a determined orientation with respect to the fastener 3.

Advantageously, each sensing element 18 is applied, directly or indirectly (for example by means of the respective rigid part 15) , on an application surface 19 of the fastener 3. Preferably, the application surface 19 is flat and transversal, in particular perpendicular, to the longitudinal axis Zl.

According to the example illustrated in Figs. 1 to 5, the sensing element 18 is an accelerometer, which is configured to emit signals depending on any vibrations that can affect the fastener 3.

Advantageously, the accelerometer 18 has a reference system XI, Y1 (Fig. 3) which is superimposed on the reference system X, Y on the plane n of the fastener 3. Advantageously, the recess 7 is configured so that the orientation of the accelerometer 18 is unique and ensures the correct positioning of the axes of the reference system XI, Y1.

According to the variant illustrated schematically in Figs. 6A to 6E, the monitoring portion PM comprises a plurality of sensing elements 18 applied to the fastener 3. In particular, the sensing elements 18 are strain gauges 18d. The number and the mutual arrangement of the strain gauges 18d are variable. The figures illustrate, by way of non-limiting example, solutions with: two strain gauges 18d evenly distributed around the longitudinal axis Z1 (Fig. 6A) ; three strain gauges 18d evenly distributed around the longitudinal axis Z1 (Fig. 6C) ; a central strain gauge 18d (6B) ; two strain gauges 18d evenly distributed around the longitudinal axis Z1 and a central strain gauge 18d (Fig. 6D) ; three strain gauges 18d evenly distributed around the longitudinal axis Z1 and a central strain gauge 18d (Fig. 6E) . According to a variant, not illustrated, an accelerometer is provided alternatively or in addition to the central strain gauge 18d.

Advantageously, a monitoring portion PM comprising one or more strain gauges 18d applied, as in the examples illustrated in Figs. 6A to 6E, to the head of the 6 of the fastener 3 allows measurement of: the shear and/or bending and/or axial load to which the fastener 3 is subjected without making holes in the shank 4 of the fastener 3 itself. Therefore, this allows fasteners 3 of small size (for example M6 screws) to be monitored without affecting the resistant section of the shank 4. Moreover, advantageously, the position of each strain gauge with respect to the longitudinal axis Z 1 is determined so as to detect the deformation signals in the points in which these phenomena are generated in an ampli fied manner ( depending on the type of the fastener 3 and on the speci fic application) . For example , the distribution of the strain gauges 18d as illustrated in Figs . 6A to 6E (whose radial distance from the longitudinal axis Z 1 depends on the speci fic application) allows deformations on the head 6 of the screw 3 in the 10~⁶ meter/meter range ( or micrometer/meter, also generally indicated as ps ) to be detected . Therefore , a monitoring portion PM comprising strain gauges 18d distributed on the head 6 of the screw 3 as illustrated in Figs . 6A to 6E allows the use of strain gauges 18d with degree of accuracy in the 10~⁶ meter/meter range (micrometer/meter, or ps ) and of common use .

According to a variant , not illustrated, a plurality of sensing elements 18 di f ferent in type from each other ( for example an accelerometer in combination with a temperature sensor, etc . ) can be simultaneously applied on the fastener 3 according to the type of phenomena to be measured .

Each sensing element 18 communicates , in particular via the rigid measuring part 151 and/or the flexible part 161 , with the processing portion PE .

Advantageously, the processing portion PE comprises one or more electronic parts of choice . For example , the rigid processing part 1511 comprises : an electronic ampli f ication/conditioning part 135 of the signal ; and an electronic storage part 136 .

The processing portion PE is configured to collect , convert the signals received from the sensing elements 18 into data referring to parameters , which depend on the operating conditions of the fastener 3 . The processing portion PE is capable of reprocessing the data according to prede fined logics .

The processing portion PE is connected to the connection portion PC through the flexible part 1611 .

The figures illustrate solutions in which the connection portion PC is via cable . In particular, the rigid connection part 15I I I has a plurality of holes 20 , which are coated with conductive material . The connector 12 comprises a plurality of pins 21 , each of which is welded inside a respective hole of the rigid connection part 15I I I . According to the example illustrated in the figures , four holes 20 and four respective pins 21 are present . The number of holes and of pins 21 is variable .

The connector 12 further comprises contact elements 22 , for example pins , for connection to external cables (not illustrated) .

The connector 12 further comprises a body 23 that houses within it the pins 21 and the contact elements 22 . The body 23 is axisymmetric with respect to a longitudinal axis . The body 23 has a flange 24 that protrudes radially outwards at one end . The body 23 is externally threaded .

The cap 11 is an axisymmetric body with respect to a longitudinal axis . The cap 11 has an internal cavity 25 and comprises a flange 26 and a threaded portion 27 . The internal cavity 25 communicates axially with the outside through axial openings identi fied hereunder with 01 and 02 . The opening 01 is produced through the end at the threaded portion 27 , the opening 02 is produced through the opposite end . The threaded portion 27 is external and is produced at an axial end . The shape , si ze and arrangement of the threaded portion 27 are variable . The cap 11 has been screwed onto the fastener 3 by means of the threaded portion 27 . The control system 2 comprises a ring nut 28 . The ring nut 28 is screwed onto the threaded portion 23 of the connector 12 that protrudes outside the cap 11 . The ring nut 28 axially constrains the connector 12 to the cap 11 . Due to the use of the ring nut 28 , the electronic unit 10 is not rotated during fixing of the control system 2 on the fastener 3 .

Gaskets g are arranged between : the cap 11 and the fastener 3 ; the cap 11 and the connector 12 .

According to a variant , not illustrated, the connector 12 has no contact elements 22 ; for example , the connector 12 is configured to allow a wireless connection with the outside world . The connector 12 can be made of a non-metallic material . The connector 12 can comprise means for receiving and/or transmitting wireless data .

According to the example illustrated in Figs . 1 and 4 , the control system 2 further comprises a support frame 14 that is configured to orient the rigid processing part 1511 , as will be better illustrated hereunder . The frame 14 is an axisymmetric body with respect to a longitudinal axis . The frame 14 has an internal cavity 30 configured to house , at least partially, the electronic unit 10 . The frame 14 has an stop element 31 . According to the example illustrated, the stop element 31 is an oblique end surface of the frame 14 transversal to the longitudinal axis . Advantageously, the stop element 31 is not perpendicular to the longitudinal axis . In other words , the stop element 31 is inclined with respect to the longitudinal axis by an angle a=/90 ° .

According to the example illustrated in Fig . 1 , the electronic unit 10 is electromagnetically connected to the connector 12 and the measuring portion PM is applied to the fastener 3 within the recess 7 . Advantageously, at least part of the measuring portion PM is applied to a flat surface . Advantageously, the axes XI , Y1 of the rigid measuring part 151 are aligned with the axes X and, respectively, Y of the fastener 3 to allow the rigid measuring part 151 to be inserted into and housed within the recess 7 .

Advantageously, the flexible parts 16 of the electronic unit 10 are bent so as to obtain a " sandwich" structure . In this way, the dimensions on a plane ( in the example illustrated the plane n perpendicular to the longitudinal axis Z 1 of the fastener 3 ) are greatly reduced . The bends of the flexible parts 16 make it possible to obtain an electronic unit 10 with limited radial dimensions , instead of one with larger axial dimensions . This makes it possible to reduce the radial dimensions of the cap 11 . Furthermore , the division of the various parts of the electronic unit 10 allows the dimensions at the area of contact with the fastener 3 to be minimised . This makes it possible to use the control system 2 to monitor fasteners 3 of very small si ze .

Advantageously, the electronic unit 10 passes through the frame 14 . In particular, the rigid connection part 15I I I and the flexible part 1611 pass through the frame 14 . Advantageously, the rigid process ing part 1511 is positioned in contact against the stop element 31 of the frame 14 . The rigid processing part 1511 can be coupled ( in a known way) to the stop element 31 . Advantageously, the presence of the frame 14 and, in particular, of the stop element 31 allow the rigid processing part 1511 to be inclined with respect to the longitudinal axis . This allows the correct positioning and housing of the bends of the flexible parts 16 suitably bent . The frame 14 guides the bending and insertion of the flexible parts 16 , ensuring their correct positioning . In fact , bends that are too narrow could compromise the integrity of the flexible parts 16 . Moreover, advantageously, the presence of the frame 14 increases the stability of the rigid processing part 1511 during use and facilitates assembly . The assembly formed by the electronic unit 10 and by the frame 14 is inserted into the cap 11 through the opening 01 . The connector 12 passes partially through the opening 02 . The flange 20 of the connector 24 is housed within the cavity 25 of the cap 11 . Advantageously, the cap 11 is free to rotate with respect to the connector 12 and to the electronic unit 10 . In other words , when the cap 11 rotates it does not rotate the connector 12 and the electronic unit 10 .

According to the variant illustrated in Fig . 5 , the control system 2 has no frame 14 . In the variant illustrated in Fig . 5 , all the elements in common with the solution illustrated previously have the same reference numbers and are considered as contained herein, without being repeated for the sake of brevity .

According to the variant illustrated in Fig . 5 , the fastener 3 is a stud of suitable si ze to house at least part of the electronic unit 10 . In this solution, in addition to the description provided previously in relation to the recess 7 , the fastener 3 ' has an indentation 33 that is staggered along the longitudinal axis Z 1 with respect to the recess 7 so as to obtain two planes nl and n2 distributed in a determined way . The rigid measuring part 151 is applied on the plane nl and the rigid processing part 1511 is applied on the plane n2 .

Advantageously, each rigid part 15 of the electronic unit 10 can be fixed, for example glued, to a respective plane and/or stop element .

According to a variant , not illustrated, the communication portion PC is of wireless type ; in other words , the communication portion PC operates in wireless mode . The communication portion PC is configured to exchange data, in particular to transmit and receive data and electromagnetic signals S , with an external control system, directly and/or indirectly, i . e . , through an exchange network . For the operating modes for "exchanging data and electromagnetic signals S directly" in wireless mode , reference is made to the teachings of WO 2023281429 Al , the content of which is considered incorporated herein for the sake of brevity .

Advantageously, the electronic unit 10 comprises a rechargeable battery 138 . In the example , this is shown arranged at the processing portion PE , but its position is variable . According to a variant , not illustrated, the rechargeable battery is arranged at the rigid connection part 15I I I and is wirelessly rechargeable .

In the case of wireless data exchange , the control system 2 can comprise , arranged at the electronic unit 10 and/or the connector 12 connected to the connection portion PC of the electronic unit 10 , an NFC transmitter/receiver , in particular capable of exchanging data and electromagnetic signals with other NFC transmitters/receivers of other devices (not illustrated) . Advantageously, the NFC transmitter/receiver communicates with the NFC transmitter/receiver of a smartphone/ tablet or similar devices .

I f data is exchanged in wireless mode , the control system 2 can comprise , arranged at the electronic unit 10 and/or the connector 12 connected to the connection portion PC of the electronic unit 10 , one or more of the following communication systems :

- near wireless (which generally operates within a range of a few millimeters ) , for example with the inductive or capacitive principle ( for example , the use of an NFC or RFID transmitter/receiver ) ; and/or

- radiofrequency (which generally extends up to a few meters ) , for example a Bluetooth system, in particular of the type known as Bluetooth Low Energy (BLE ) or Wi-Fi ; and/or - optical , for example an infrared system; and/or a mobile terminal device , i . e . , a radio interface , for radiotelephony communication on the radio interface for access to one or more exchange networks T , in particular telecommunication networks , for example : landline network, cellular network, data network, Internet network, GSM, GPRS , UMTS/EDGE , VSF-Spread, OFDM, GPS .

I f the wireless communication part comprises a mobile terminal device the control system 2 can comprise , arranged at the electronic unit 10 and/or the connector 12 connected to the connection portion PC of the electronic unit 10 , a physical or virtual sim ( also known commercial ly as esim®, or embedded sim) for access to an exchange network of speci fic telephone operators and/or access to the Internet and to the cloud .

Advantageously, the monitoring system 1 , 1 ' , 1 ' ' of the type described above allows particularly accurate detection of the signals to be measured due to application of the sensing elements 18 directly on a flat surface 19 of the fastener 3 . Moreover, it has been found that the suitable positioning of sensing elements 18 on flat surfaces of the head 6 of a screw 3 allows reliable signals to be obtained for subsequent measurements of deformation and/or bending and/or of pull and/or shear exerted on the screw 3 .

Advantageously, the fact of arranging the rigid parts 15 of the electronic unit 10 against flat stop surfaces or elements ( 31 , nl , n2 ) means that the electronic unit 10 can be made particularly stable . Advantageously, in the case of fixing by gluing, the cohesion between the sensing element 18 and the fastener 3 is particularly stable , strong and quick to produce . This is particularly advantageous for correct mechanical stability of the coupling between sensing element 18 and fastener 3 in the case in which the fastener 3 is installed on a mechanical apparatus subj ected to considerable vibrations . According to some variants , not il lustrated, the sensing element 18 can be fixed to the fastener 3 using dif ferent solutions , for example : by screwing; by welding; by producing interference fits ; or by producing fixing solutions equivalent to those listed .

Advantageously, the frame 14 allows one or more rigid parts 15 of the electronic unit 10 to be oriented with respect to the longitudinal axis Z of the fastener 3 . This allows for better housing of the bends of the flexible parts 16 that protrude at the sides of the rigid parts 15 . In other words , the inclination provided by the frame 14 advantageously allows the flexible parts 16 to be bent in the shape of an S and the correct formation of the " sandwich" structure to be obtained, while remaining within the dimensions of the diameter of the head 6 of the screw 3 . Moreover, the frame 14 gives greater structural strength to the rigid part 15 , preventing it from bending during use .

Advantageously, the monitoring system 1 , 1 ' , 1 ' ' according to the present invention, due to the division of the electronic unit 10 into a plurality of rigid 15 or flexible 16 parts axially distributed, allows the radial dimensions to be minimised at the interface with the fastener 3 , 3 ' . In fact , only the ( rigid and/or flexible ) components of the electronic unit 10 strictly necessary to perform the desired measurements can be applied at the interface with the fastener 3 , 3 ' .

Advantageously, the monitoring system 1 , 1 ' , 1 ' ' according to the present invention does not require the presence of speci fic cavities or housings in the shank 4 of the fastener 3 , 3 ' . In other words , advantageously, the fastener 3 , 3 ' is solid at the areas subj ected to greater stres s . This makes it possible to guarantee the mechanical integrity of the fastener 3 without af fecting the resistant section of the shank 4 .

Advantageously, the monitoring system 1 , 1 ' ' according to the present invention can be produced with any type of fastener 3 , even with commercial and/or very small fasteners 3 , which could not house sensing elements within their shank 4 , as the diameter is too small . In particular, the monitoring system 1 can be applied to commercial and/or very small fasteners 3 with a head having an axial thickness that is too small to accommodate anything except the coupling between sensing element 18 and fastener 3 and the seal via O-Ring . Advantageously, the monitoring system 1 , 1 ' ' of the type described above can be produced using commercial fasteners 3 and/or those already in use .

Modi fications and variations can be made to the monitoring system described and illustrated herein, without however departing from the scope of protection of the present invention, as defined in the appended claims .

Claims

1. A monitoring system comprising a control system (2) and a fastener (3) , in particular a screw or a stud, configured to fasten two or more mechanical components of a mechanical apparatus to each other; wherein the fastener (3) comprises a shank (4) , which has a longitudinal axis (Zl) , and a head (6) , which is configured to interact, in use, with a tightening tool; wherein the control system (2) comprises, in turn, one or more sensing elements (18, 18d) ; wherein each sensing element (18, 18d) can be selected within a group of sensing elements different in type from each other; wherein each sensing element (18, 18d) is applied to a transversal surface (nl, n2) , in particular perpendicular, to the longitudinal axis (Zl) of the fastener (3) .

2. A monitoring system according to claim 1, wherein each sensing element (18, 18d) is applied to the head (6) of the fastener (3) ; in particular, the shank (4) of the fastener (3) is solid, in particular has no internal cavities and/or housings.

3. A monitoring system according to claim 1 or 2 and comprising a plurality of sensing elements (18, 18d) which are evenly distributed around the longitudinal axis (Zl) of the fastener (3) .

4. A monitoring system according to any of the preceding claims , and comprising a sensing element (18, 18d) centred on the longitudinal axis (Zl) of the fastener (3) .

5. A monitoring system according to any of the preceding claims, wherein one or more sensing elements (18, 18d) are strain sensors .

6. A monitoring system according to any of the preceding claims, wherein a sensing element (18, 18d) is an accelerometer.

7. A monitoring system according to claim 6, wherein the accelerometer (18, 18d) is oriented in a determined way with respect to the longitudinal axis (Zl) of the fastener (3) ; in particular , the fastener (3) has a recess (7) in the head (6) ; wherein the recess (7) is shaped with reference to two axes (X, Y) of a plane (n) perpendicular to the longitudinal axis (Zl) of the fastener (3) ; wherein the accelerometer (18, 18d) is housed within said recess (7) .

8. A monitoring system according to any of the preceding claims; wherein the control system (2) comprises, in turn, an electronic unit (10) , at least partially flexible; in particular, the electronic unit (10) is a rigid-flex printed circuit board; wherein the electronic unit (10) comprises: a measuring portion (PM) , which is configured to emit signals, in particular depending on the conditions of the fastener (3) ; a processing portion (PE) , which is connected to the measuring portion (PM) and is configured to convert and process the signals received from the measuring portion (PM) itself; and a connection portion (PC) , which is connected to the processing portion (PE) ; the connection portion (PC) is configured to exchange data and/or electromagnetic signals with the outside world via cable or wireless; wherein said measuring portion (PM) is applied to the head (6) of the fastener (3) and comprises one or more sensing elements (18, 18d) .

9. A monitoring system according to claim 8, wherein said measuring portion (PM) can be at least partially rigid and/or flexible .

10. A method to monitor, by means of a control system (2) , a fastener (3) comprising a shank (4) , which has a longitudinal axis (Zl) , and a head (6) , which is configured to interact, in use, with a tightening tool; wherein the control system (2) comprises, in turn, one or more sensing elements (18, 18d) ; wherein each sensing element (18, 18d) can be selected within a group of sensing elements different in type from each other; wherein, each sensing element (18, 18d) is applied on a transversal surface (nl, n2) , in particular perpendicular, to the longitudinal axis (Zl) of the fastener (3) ; the method comprising the step of detecting, by means of said sensing elements (18, 18d) , one or more signals related to the instantaneous state of the fastener (3) .

11. A method according to claim 10, wherein one or more sensing elements (18, 18d) are flexible; in particular, the control system (2) comprises a plurality of strain gauges (18d) distributed around the longitudinal axis (Zl) of the fastener (3) ; wherein the step of detecting comprises measuring signals related to possible deformations of the head (6) of the fastener (3) ; in particular, each strain gauge (18d) allows the detection of deformations in the 10~⁶ meter/meter range.

12. A method according to claim 11, wherein the signals related to possible deformations of the head (6) of the fastener (3) are used to measure the shear and/or the axial load and/or the bending exerted on the fastener (3) itself.

13. A method according to any claim from 10 to 12, wherein, the control system (2) comprises an accelerometer (18) ; wherein the step of detecting comprises measuring signals related to vibrations to which the fastener (3) is subjected.