Instrument assembling screw

Abstract

The invention relates to an assembly screw comprising at least a threaded portion (12A) and a non-threaded portion (12C), the non-threaded portion being provided with a strain gauge (22) sensitive to the instantaneous elongation of the non-threaded portion and an RFID tag (24) connected to the strain gauge by a wired link, the fitting screw allows wireless transmission of resistance values for the strain gauge representing instantaneous elongation.

Description

Technical Field

[0001] The invention relates to the field of controlled tightening, more particularly to the kind of manual wrenches, such as torque wrenches with a release mechanism or direct-reading (mechanical or electronic) torque wrenches. Background Art

[0002] The tightening of screw components can be controlled in different ways, namely by measuring the torque (clamping force), the angle of rotation (conversion of screw body elongation to thread pitch) or the elongation of the screw.

[0003] Angular tightening is widely used in the automotive industry. This can be achieved with a manual spanner that includes a device for measuring the tightening angle. Elongation tightening is used for long screws also called drawbars (manual, hydraulic or thermal elongation methods). Torque tightening, on the other hand, is the most common method using a spanner with a release mechanism or an electronic spanner and has the advantage of being simple to use. However, its main disadvantage is that for a given tightening torque, the forces acting on the screw components and the resulting mechanical deformations vary greatly, with a significant dispersion of the apparent friction coefficients (thread, screw head bearing, nut surface, locking element, etc.), torsion of the screw body, etc.

[0004] For example, for lubricants based on polytetrafluoroethylene (Teflon), such as those used in low-temperature engines, experience leads to a dispersion of this coefficient taken into account when dimensioning screw or bolt connections of about 300%. The magnitude of this dispersion leads to many difficulties or even impossibility when dimensioning the setpoint torque. Specifically, at the design stage and for torque tightening, it is necessary to take into account the limits of the range of variation of the friction coefficient, i.e. a low coefficient that determines the mechanical strength of the assembly and a higher coefficient responsible for the tightening quality of these connections (sufficient compression of the seal, sufficient tightening of the flange, etc.).

[0005] This situation is unsatisfactory since it leads to an overdimensioning of the connection, which is disadvantageous both from the point of view of quality and from the point of view of the mechanical behavior of the screw components over time (fatigue, loosening, etc.).

[0006] Furthermore, it is necessary to take into account the mechanical deformation of the screw component caused by the tension applied to the screw component. Specifically, during the tightening operation, a screw component initially has an elastic (i.e. reversible) deformation region, in which the deformation varies linearly with the force, and then, if the tightening continues, a plastic (i.e. irreversible) deformation region, in which the deformation varies more and more rapidly with the stress, ending in failure. As a result of this behavior, torque tightening resulting in very dispersed tensions must preferably be performed in the elastic deformation region of the screw component far from the elastic limit.

[0007] The wrenches currently available allow to control the torque alone (wrenches with release mechanism, direct reading wrenches or ultrasonic wrenches), or to control the torque and angle or extension simultaneously, in order to tighten the screw component to the desired set value for the torque and / or angle or extension. The torque tightening devices also have complex processing means, making it possible to increase the precision of the tightening in successive stages.

[0008] However, in all these cases, the tightening value is guaranteed by the wrench alone, but during use, the wrench can unfortunately lose precision. In addition, it can happen that the wrench is incorrectly calibrated after human error or, worse still, that tightening is neglected.

[0009] This control by means of a wrench alone also appears unsatisfactory and an alternative solution is therefore needed which ensures in any case the complete tightening of these fastenings or bolted joints by knowing the instantaneous tension exerted on the screw component, which is a parameter that determines the quality of the fastening and its durability. Summary of the invention

[0010] Therefore, the main purpose of the present invention is to solve the above mentioned problems by allowing real time knowledge of the tightening torque value. Another purpose is to ensure this knowledge once the coupling has been made and may become inaccessible. Another purpose is to be able to be informed at any time of any loss of tightening.

[0011] These objects are achieved by an assembly element comprising at least a threaded portion and a non-threaded portion, characterized in that the non-threaded portion is equipped with a strain gauge sensitive to the instantaneous elongation of the non-threaded portion and an RFID tag connected to the strain gauge by a wired link so as to allow wireless transmission of the resistance value of the strain gauge representing the instantaneous elongation.

[0012] Thus, by the instantaneous extension of the extension section of the relay screw, the tightening torque can be controlled at any time, regardless of whether the assembly screw is accessible or not.

[0013] The assembly screw may include two threaded end portions separated by a non-threaded central portion.

[0014] According to contemplated embodiments, a strain gauge may be bonded or printed onto a non-threaded portion of the assembly screw, and an RFID tag may be bonded or printed onto a non-threaded portion of the assembly screw.

[0015] The strain gauge is advantageously a uniaxial tensile resistance strain gauge linked to the RFID tag by wires.

[0016] The RFID tag advantageously comprises an active memory chip and a UHF antenna.

[0017] When the strain gauge and RFID tag are printed, the wired link is also printed on the non-threaded portion of the mounting screw.

[0018] The present invention also relates to a system for determining the tightening torque of an assembly screw, the system comprising the assembly screw as described above, and an RFID reader comprising an RFID antenna and an RFID chip for receiving a resistance value transmitted by a strain gauge of the assembly screw, the system further comprising a processing module for determining the tightening torque based on the resistance value, and a display for displaying the determined tightening torque.

[0019] Advantageously, the RFID reader includes an audible or luminous device to provide an alarm in the event of a loss of fastening. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Other characteristics and advantages of the invention will become apparent from the description given below, with reference to the accompanying drawings, which show, without any limitation, an exemplary embodiment and in which:

[0021] Figure 1 is a cross-sectional view of a wrench used to tighten the assembly screw, and

[0022] Figure 2 An instrument mounting screw according to the present invention is shown. DETAILED DESCRIPTION

[0023] The principle of the invention is based on the instrumentation of an assembly element, screw, stud or bolt, in order to know in real time the characteristics representing the tightening torque value, thus transmitting it to an external processing module capable of making use of it.

[0024] Figure 1 An embodiment of a wrench 10 for tightening an assembly screw 12 for assembling a first component 14 and a second component 16 is shown, the second component being threaded to receive a threaded portion 12A of the assembly screw. A washer 18 is installed between the head 12B of the assembly screw and the first component 14. The rotation angle is measured by a measuring device 20, which includes a clamping bushing 20A that interacts with the head 12B of the assembly screw and measures the differential rotation between the bushing 20A and the first component 14 through a spring 20B provided around the outer circumference of the bushing, and a Teflon® tube 20C provided with an anti-slip ring 20D, inserted between the spring 20B and the upper surface of the first component 14. The Teflon® tube can generate a low friction coefficient between the moving parts to avoid affecting the tightening torque.

[0025] Of course, this measurement configuration by means of a spring is not limiting and optical, magnetic or electrical (rheostat type) measurements are also quite possible instead of the spring and the clamping bushing.

[0026] Regardless of the chosen configuration, the wrench also comprises input means for defining a set value for tightening, and processing means for calculating the tightening torque based on the rotation angle transmitted by the measuring means 20 and informing the operator (generally by an acoustic and / or luminous signal) when the initially defined set value has been reached. Reference is made to application FR 2 852 879 for more details on the calculations involved in the determination of this tightening torque based on the rotation angle.

[0027] However, as explained in the introduction, once the connection has been made and the wrench has been removed, it is not possible to further control the timing of the tightening torque and in particular any loss of tightening.

[0028] Therefore, according to the present invention and Figure 2 As shown, the non-threaded portion 12C of the assembly screw 12 is equipped with a strain gauge 22 and an RFID (Radio Frequency Identification) tag 24 connected to each other by a wired link 26. The RFID tag is intended to interact remotely with an advantageously portable RFID reader 28, comprising an RFID antenna / chipset 30 connected to a processing module 32, which is itself connected to a display 34 and / or a speaker. In the event of a loss of tightening, the display and / or the speaker can constitute an audible and / or luminous warning device for the operator. The assembly screw and the RFID reader set form a system for determining the tightening torque of an assembly screw, the assembly screw comprising at least a screw portion and a non-threaded portion, so as to allow the wireless transmission of the resistance value of the strain gauge representing the elongation of the assembly screw.

[0029] Strain gauges (resistance wire extensometers, conventionally manufactured by photolithographic processes, from a metal sheet of a few microns and an electrical insulator of the polyamide type) are preferably bonded to this non-threaded portion in order to detect the instantaneous elongation which causes a change in the resistance of the strain gauge. Bonded resistance strain gauges, in particular uniaxial tension strain gauges, are well known in the instrumentation industry (characterized by their dimensions, resistance to thermal / corrosive environments and bonding to different substrates). However, strain gauges can also be produced directly by printing on the shank (non-threaded portion) of the screw itself.

[0030] The RFID tag that can be similarly glued to the non-threaded part of the assembly screw comprises an antenna 24A connected to a processing module 24B (so-called RFID memory chip), which comprises a memory and transmission / reception means for interacting with corresponding means of an RFID reader 28. Adhesive RFID tags are known (characterized by size, integration / substrate, distance detected by the reader, storage capacity, active or passive nature). However, the tag can also be produced directly by printing on the shank (non-threaded part) of the screw itself. Depending on the frequency environment and the detection distance (power characterized by the frequency range: low (low frequency, LF 125 kHz) / high (high frequency, HF 13.56 MHz) / ultra-high (ultra-high frequency, UHF 433 and 860-960 MHz) / ultra-high (super-high frequency, SHF 2.45 GHz)), different frequency ranges and associated antennas will be used.

[0031] The strain gauge and the RFID tag are linked by two measuring wires forming a wired link 26. When the two elements mentioned above are printed, the wired link is advantageously also printed.

[0032] Placing a strain gauge on the shank (non-threaded portion) of the assembly screw makes it possible to determine a resistance value based on the instantaneous elongation of this shank, which value will be stored in the memory of the RFID chip and can therefore be read by the RFID reader at any time. Suitable processing known per se will allow the processing module 32 of the RFID reader to infer the tightening torque from this resistance value and present it to the operator on the display 34 of the RFID reader.

[0033] Depending on the nature of the RFID chip, it is possible to envisage active or passive, automatic feedback of information to an RFID reader, in particular in the event of loss of tightening, with an audible and / or luminous alarm at the RFID reader. The code associated with the torque information will precisely indicate the position of the screw in the bolt assembly.

[0034] It should be noted that although the previous description relates to conventional screws, it is obvious that it also applies to headless screws (or studs) with double threads, the non-threaded central part between the two threads of which will be equipped with a strain gauge and RFID tag as described above.

Claims

1. An assembly screw (12) comprising at least a threaded portion (12A) and a non-threaded portion (12C), the non-threaded portion being provided with a strain gauge (22) sensitive to the instantaneous elongation of the non-threaded portion (12C) and an RFID tag connected to the strain gauge (22) via a wired link (26) so as to allow wireless transmission of a resistance value of the strain gauge representing the instantaneous elongation, characterized in that The strain gauge (22) is printed on the non-threaded portion (12C) of the assembly screw, and the RFID tag (24) is printed on the non-threaded portion (12C) of the assembly screw (12).

2. An assembly screw (12) according to claim 1, comprising two threaded end portions separated by a non-threaded central portion.

3. The assembly screw (12) according to any one of claims 1 or 2, wherein: The wired link (26) is printed on the non-threaded portion (12C) of the mounting screw.

4. The assembly screw (12) according to any one of claims 1 to 3, wherein: The strain gauge (22) is a uniaxial tensile resistance strain gauge connected to the RFID tag (24) via a wire.

5. The assembly screw (12) according to any one of claims 1 to 3, wherein: The RFID tag (24) includes an active memory chip (24B) and a UHF antenna (24A).

6. A system for determining the tightening torque of an assembly screw, the system comprising an assembly screw (12) as claimed in any one of claims 1 to 5, and an RFID reader (28), the RFID reader (28) comprising an RFID antenna and an RFID chip (30) for receiving a resistance value transmitted by a strain gauge (22) of the assembly screw (12), the system further comprising a processing module (32) for determining the tightening torque based on the resistance value, and a display (34) for displaying the determined tightening torque.

7. The system according to claim 6, wherein: The RFID reader (28) includes an audible or luminous device to provide an alarm in the event of a loss of fastening.

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