EP1462220B1 - Controlled wrench - Google Patents

Abstract

The wrench has a microprocessor (1) to calculate an instantaneous traction effort on a nut based on instantaneous values of applied coupling and angle of rotation measured by two sensors (2, 3), and recorded nut characteristics. A software unit in the microprocessor finds the traction effort based on detection of a transition from an elastic range to a plastic range, during the nut tightening.

Description

Field of the invention

The present invention relates to the field of controlled tightening and more particularly to manual tightening wrenches, such as torque wrenches, comprising electrical or electronic measuring and processing means for informing the operator that a set value is reached. Such a key, according to the preamble of claim 1, is described in DE 44 04419.

Background of the invention

The tightening control of fasteners can be implemented with different methods, namely by measuring the torque, the angle or the clamping force. The most commonly used method is torque tightening, using either triggering keys or electronic keys. Corner clamping is widely used in the automotive industry. This can be implemented with a manual tightening wrench which comprises means for measuring the clamping angle. Tightening with effort has been used so far only on very specific links. For example, there are keys that allow to tighten the effort but only up to the elastic limit. Other known tightening wrenches allow a tightening force in a wider range but then require tightening in three successive steps (ie tightening until an estimate of the target tightening, then complete loosening and finally tightening until 'to the calculated value), which can be detrimental to the integrity of the link. In these applications, the clamping is controlled by means of ultrasonic measuring systems or hydraulic tensioners.

Torque tightening has the advantage of being simple to use. On the other hand, it presents a major disadvantage: for a given tightening torque, the force on the fasteners varies greatly, following the significant dispersion of the coefficient of friction. This is illustrated schematically in FIG. 9. In this figure, it can be seen that for a given setpoint torque C _applied , due to the dispersion of the apparent coefficient of friction [ f _min , f _max ], a dispersion [F _min , F _max ] of the tensile force F on the fasteners and, consequently, of the mechanical deformation.

For Teflon®-based lubrications for example, such as those used on cryogenic engines, the experiment led to a dispersion of the order of 300% of this coefficient being taken into account when dimensioning the screwed connections. The importance of this dispersion is at the origin of many difficulties, even impossibilities, of sizing of the set torque. Indeed, in design and for torque tightening, the extreme limits of the coefficient of friction variation range must be taken into account: the low coefficients condition the mechanical strength of the assembly, while the highest coefficients are responsible for the quality of the tightening of the connections (sufficient crushing of the joints, sufficient tightening of the flanges, etc ...). Such a situation is not satisfactory because it leads to an over-dimensioning of the links which is detrimental both from the point of view of the mass, as well as with regard to the mechanical behavior of the fasteners over time (fatigue, loosening, etc.). .).

On the other hand, it is necessary to take into account the mechanical deformation of the fasteners resulting from the tensile force applied to it. Indeed, during a clamping operation, it was initially an elastic deformation regime (ie reversible), where the deformation varies linearly with the effort, then, if we continue the tightening, a regime of plastic deformation (ie irreversible), where the deformation varies more and more rapidly with the stress, to finish at break. From this behavior it follows that torque tightening, leading to a very dispersed tensile force, must preferably be performed in the field of elastic deformations of the fasteners far from the elastic limit.

There are currently clamping wrenches for controlling either the tightening torque alone, as described in US Pat. No. 3,710,874, or at the same time the tightening torque and the angle of rotation in order to effect a tightening of fasteners corresponding to a target value for the tightening torque and / or the angle of rotation. Such a device is described in particular in the European patent application EP 1 022 097. Finally, there are dynamometric clamping devices with elaborate processing means that can increase the accuracy of clamping. Such a device is described in particular in French patent application FR 2 780 785. However, with this type of device, the tightening control can only be performed with a specific tightening procedure comprising intermediate clamping and loosening steps for reach a target value.

In summary, none of the known clamping devices does not mention a manual tightening wrench for determining the instantaneous tensile force exerted on the fasteners, which parameter determines the quality of the clamping and its resistance over time. On the other hand, there are no devices that allow to resume directly and without risk an interrupted tightening.

Object and summary of the invention

The present invention aims to overcome the aforementioned drawbacks and to achieve a tightening key that avoids oversizing the links to screw while allowing clamping in one step. The invention also aims to achieve a key that allows to resume without difficulty an interrupted tightening before reaching the target value.

These aims are achieved by means of a tightening wrench comprising an instantaneous torque measurement means applied, a head capable of cooperating with a fastener element, said head being equipped with a means of instantaneous measurement of the angle of rotation, and input means for recording characteristics of the fastener element and a set value for tightening, characterized in that the key further comprises processing means for calculating the instantaneous pulling force on the fastener element in accordance with the instantaneous measured torque and angle values as well as the characteristics of the bolted fastener.

Thus, the instantaneous pulling force is directly calculated during tightening which allows either to be able to directly perform a controlled clamping force, or to have the value of the effort at the end of tightening. The quality of the clamping can therefore be controlled directly during the tightening or at the end of the latter. Over-sizing of the links can thus be avoided.

The tightening key of the present invention also makes it possible to obtain and memorize a set of information on the apparent coefficient of friction of the connection, in particular the evolution of this coefficient as a function of speed and time, as well as the difference between static and dynamic friction coefficient. Access to this type of information relating to the coefficient of friction makes it possible to detect any anomalies such as for example seizing the link if the coefficient of friction detected is too great.

The processing means calculate the instantaneous force in real time, which makes it possible to perform the tightening of the fastener element in a single step.

According to one characteristic of the invention, the processing means comprise software means for calculating the instantaneous coefficient of friction of the fastener element or for resuming an interrupted tightening before reaching the setpoint value.

According to another characteristic of the invention, the processing means comprise software means for automatically detecting, during the tightening operation, the transition from the elastic domain to the plastic domain and to calculate the instantaneous pulling force on the fasteners. depending on the result of the detection of the clamping range.

According to one embodiment of the invention, the means for instantaneous measurement of the angle of rotation comprises a bushing adapted to cooperate with the fastener element, a bearing element formed of a material with a low coefficient of friction for do not disturb the measurement of the tightening torque and a spring interposed between the bushing and the support element. The end of the bearing element intended to be in contact with the fastener element is provided with a material with a high coefficient of friction, such as rubber, so that the portion of the sleeve used to measure the Rotation angle builds without turning on the threaded fastener element to tighten.

The key may furthermore comprise storage means and a display device for storing and indicating information relating to the tightening such as the values of the torque and the angle of rotation measured during the tightening, the tensile force calculated during the tightening, the static and dynamic coefficients of friction calculated during the tightening, as well as the tightening range.

The setpoint may correspond to a tensile stress, a torque, or a predetermined clamping angle. The device comprises warning means controlled by the means of processing when the calculated or measured value reaches the setpoint.

According to the invention, the instantaneous torque measurement means applied, the input means, the processing means and, where appropriate, the display device, are arranged in a handle connected to the head of the key to enable an operator to perform the tightening manually.

Brief description of the drawings

• la figure 1 est une vue schématique du circuit de contrôle de la clé de serrage conformément à un mode de réalisation de l'invention,
• la figure 2 est une vue en perspective et en coupe partielle d'un mode de réalisation de la clé selon l'invention utilisé pour le serrage d'une liaison type boulon,
• la figure 3 est une courbe montrant l'évolution de l'effort de traction F(t) en fonction du couple C(t) et de l'angle de rotation θ(t) mesurés conformément à l'invention,
• la figure 4 est une courbe montrant l'allure théorique du coefficient de frottement f entre deux surfaces en contact en fonction de leur vitesse relative V,
• la figure 5 est une courbe montrant l'évolution de l'effort de traction F(t) en fonction du couple C(t) et de l'angle de rotation θ(t) mesurés en cas de serrage interrompu conformément à l'invention,
• la figure 6 est une vue en coupe d'un mode de réalisation de la clé selon l'invention utilisé pour le serrage d'une vis,
• la figure 7 est une vue en coupe partielle d'un mode de réalisation de la clé selon l'invention utilisé pour le serrage d'une liaison de type union,
• la figure 8 est une vue en coupe partielle d'un exemple de configuration de la clé selon l'invention utilisé pour le serrage d'une liaison de type raccord, et
• la figure 9 représente des courbes d'effort de traction F en fonction du couple de serrage C.

Other characteristics and advantages of the invention will emerge from the following description of particular embodiments of the invention, given by way of non-limiting examples, with reference to the appended drawings, in which:

• FIG. 1 is a schematic view of the control circuit of the tightening key in accordance with one embodiment of the invention,
• FIG. 2 is a perspective view in partial section of an embodiment of the key according to the invention used for tightening a bolt-type connection,
• FIG. 3 is a curve showing the evolution of the tensile force F (t) as a function of the torque C (t) and the rotation angle θ (t) measured according to the invention,
• FIG. 4 is a curve showing the theoretical shape of the coefficient of friction f between two surfaces in contact as a function of their relative speed V,
• FIG. 5 is a curve showing the evolution of the tensile force F (t) as a function of the torque C (t) and the rotation angle θ (t) measured in the case of clamping interrupted in accordance with the invention ,
• FIG. 6 is a sectional view of an embodiment of the key according to the invention used for tightening a screw,
• FIG. 7 is a partial sectional view of an embodiment of the key according to the invention used for clamping a union type connection,
• FIG. 8 is a partial sectional view of an exemplary configuration of the key according to the invention used for clamping a connection-type connection, and
• FIG. 9 shows tensile force curves F as a function of the tightening torque C.

Detailed description of an embodiment

The method of controlling the clamping implemented in the key of the present invention requires two types of measurements, that of the tightening torque applied and that of the rotation angle of the clamping.

Torque measurement is done conventionally as in most commercially available torque keys, ie by extensometry using strain gauge signals.

The angle of rotation is measured electrically or electronically using two concentric cylindrical surfaces of the connection. The measuring device used must generate a low coefficient of friction between the moving parts so as not to significantly affect the tightening torque taken into account in the calculations. Such a device can be for example a ball system, or tubes or bars made of materials with low friction coefficients, such as Teflon®. This last type of device for measuring the angle of rotation will be described in more detail later in this description.

Figure 1 is a block diagram which schematically illustrates the system embodied in the wrench of the present invention. The key firstly comprises programmable processing means, such as a microprocessor or computer 1, for carrying out the calculations. necessary to control the tightening according to the invention. The microprocessor also functions to manage the inputs and outputs of the system to allow an operator to control the tightening. For this purpose, the microprocessor 1 receives as input an instantaneous value C (t) of the tightening torque resulting from a device for measuring the torque 2 and an instantaneous value θ (t) of the angle of rotation given by a measuring device. measuring the angle 3. The microprocessor 1 is also connected to a data input means, such as a keyboard 4, to allow the operator to indicate the set values (ie effort, torque, angle) it wishes to achieve as well as the physical parameters of the link to be clamped which will be used in the calculations.

In order to warn the operator that the set point is reached, the system may comprise a buzzer 7 and / or a warning buzzer, such as a light-emitting diode 6, which are activated by a warning signal Saving sent by the microprocessor. The system further comprises a display device 5, connected to the microprocessor, for displaying the various data to be entered by the operator as well as all the data available at the end of clamping in digital or graphical form.

The tightening control method which is the subject of the invention implements a mathematical treatment, performed by the microprocessor, which is described below.

For the sake of simplicity, the particular case of tightening bolts is considered. This procedure is nevertheless generalizable to other types of connections screwed like screws, plugs, unions or connections, as will be explained below.

FIG. 2 illustrates an assembly operation of two parts 130 and 131 by clamping a bolt-type connection 120 comprising a screw 121 and a nut 122. The parts which are rotated during tightening are shown in solid lines whereas fixed parts are represented in broken lines. To tighten the connection 120, a clamping wrench 100 is used which comprises a head 101 disposed at the end of a handle 102. The microprocessor 1, the keyboard 4 and the display device 5 can be included in the handle 102 or be deported from the key while being connected thereto via a serial link for example.

The screw 121 comprises a threaded portion 121A connected to a head 121B which is held in position by a counter-key 104. The assembly of the parts 130 and 131 is then made by tightening the nut 122 by means of the key 100. The key 100 comprises a measurement means (not shown) of the applied tightening torque, such as for example strain gauges, which delivers an electrical signal proportional to the applied torque.

In this embodiment, the angle of rotation is measured by a measuring device 110 which comprises a clamping sleeve 112 cooperating with the nut 122. The measuring device 110 measures the differential rotation between the bushing 112 and the screw 121. For this purpose, the measuring device 110 comprises a Teflon® bar 111 interposed between the screw 121 and a spring 113 resting on the sleeve 102. A non-slip pad 114 is interposed between the contact surface of the screw and the bar. 111 so that the part of the sleeve used to measure the angle of rotation rests without turning on the screw to be tightened. The spring is used to apply a sufficient normal force on the anti-slip pad to prevent it from rotating. The angle of rotation can be measured according to several conventional techniques such as mechanical measurement (eg spiral spring), electrical measurement (eg rheostat type), optical or magnetic measurement.

avec :

x(t) :

allongement instantané du tronçon de visserie étiré

K :

raideur du tronçon de visserie étiré

E :

module d'Young de la visserie

A :

section droite du tronçon de visserie étiré

L :

longueur du tronçon de visserie étiré

p :

pas du filetage

In the case of stressed bolts in the field of elastic deformations, the instantaneous pulling force F (t) can be calculated using the following relation (1): $$\mathrm{F}\left(\mathrm{t}\right)=\mathrm{K}\mathrm{.}\mathrm{x}\left(\mathrm{t}\right)=\frac{\mathrm{E}\mathrm{.}\mathrm{AT}}{\mathrm{The}}\cdot \frac{\mathrm{\theta }\left(\mathrm{t}\right)\mathrm{.}\mathrm{p}}{360\mathrm{°}}\mathrm{}\mathit{\left(}\mathit{1}\mathit{\right)}$$

with:

x (t):

instant lengthening of stretched hardware section

K:

stiffness of stretched hardware section

E:

Young's module of the screws

AT :

straight section of stretched hardware section

L:

length of stretched hardware section

p:

not threading

The values E, A, L and P are entered by the operator using the keyboard 4. The rotation angle θ (t) is measured by the measuring device 3 of the key.

avec : $$\{\begin{array}{l}{\mathrm{d}}_2=\mathrm{d\hspace{1em}}\frac{3}{8}\cdot \sqrt{3}\cdot \mathrm{p}\\ \mathrm{tg\alpha }=\frac{\mathrm{p}}{\mathrm{\pi }\mathrm{.}{\mathrm{d}}_2}\\ {\mathrm{K}}^{\prime }=\frac{1}{\sqrt{1+{\mathrm{tg}}^2\mathrm{\alpha }+{\mathrm{tg}}^2\mathrm{\beta }}}\end{array}$$

et :

D_t :

diamètre équivalent de contact entre la rondelle et la tête de la vis

d :

diamètre du filetage

α :

angle d'hélice du filetage de la visserie

d₂ :

diamètre théorique de contact entre filets (sur flanc de filets)

β :

demi-angle du filetage de la visserie (30° pour filetage ISO M)

During tightening, the instantaneous coefficient of friction f (t) of the fasteners is calculated using relation (2) below: $$\mathrm{VS}\left(t\right)={\int }_{t^{\text{'}}=0}^{t^{\text{'}}=t}[f\left(t^{\text{'}}\right)\cdot \frac{D_t}{\mathrm{two}}+\frac{d_{\mathrm{two}}}{\mathrm{two}}\cdot \frac{K^{\text{'}}\mathit{tg}\alpha +f\left(t^{\text{'}}\right)\mathrm{.}\cos \left(\alpha \right)}{K^{\text{'}}-f\left(t^{\text{'}}\right)\mathrm{.}\sin \alpha }]\mathit{dF}\left(t^{\text{'}}\right)$$

with: $$\{\begin{array}{l}{\mathrm{d}}_{\mathrm{two}}=\mathrm{<figure-callout\; id="3"\; label="d"\; filenames="imgf0001.png"\; state="\{\{state\}\}">d</figure-callout>}\frac{3}{8}\cdot \sqrt{3}\cdot \mathrm{p}\\ \mathrm{tg\alpha }=\frac{\mathrm{p}}{\mathrm{\pi }\mathrm{.}{\mathrm{d}}_{\mathrm{two}}}\\ {\mathrm{K}}^{\text{'}}=\frac{1}{\sqrt{1+{\mathrm{tg}}^{\mathrm{two}}\mathrm{\alpha }+{\mathrm{tg}}^{\mathrm{two}}\mathrm{\beta }}}\end{array}$$

and

D _t :

equivalent diameter of contact between the washer and the head of the screw

d:

thread diameter

α:

helical angle of the screw thread

d ₂ :

theoretical diameter of contact between nets (on the side of nets)

β:

half thread angle of the screws (30 ° for ISO M thread)

For the elastic domain, the calculation of f (t) is possible because we know the value of the effort F (t), deduced from the relation (1) above and that of the torque C (t) which is measured directly .

The mechanical behavior of the clamping is represented graphically in FIG. 3, giving the variation of the tensile force as a function of the tightening torque C (t) (curve A) or the rotation angle θ (t) (curve B ).

In the case of clamping with force, the procedure consists of introducing, before tightening, the values of the following parameters: F _setpoint , p, E, A, L, D _t , d, α, d ₂ , β. Therefore, since the instantaneous force F (t) is calculated throughout the tightening operation, the resulting clamping force will be precisely the target force entered by the operator. Thus, the large dispersions on the clamping force that existed with the torque wrenches of the prior art are eliminated. Over-sizing of the links is no longer necessary since the clamping force obtained is guaranteed in advance.

Moreover, thanks to the simultaneous measurements of the torque and the tightening angle as well as to the mathematical treatment described above, the instantaneous force can be calculated in real time, which makes it possible to perform clamping with the force in one step. only step.

Figure 3 shows how it is determined the moment is reached the set value F _set to the tractive force, depending on whether the mechanical connection remains in the elastic deformation or, on the contrary, reaches the plastic deformation region .

If the connection remains in the field of elastic deformations, it suffices in this case to interrupt the clamping when the effort F (t), calculated according to the relationship (1) reaches the setpoint value F _set .

If, on the other hand, the bond plasticizes, the processing means detect, in real time, the beginning of the plasticization by reducing the slope of the curve B. From this moment, F (t) ceases to be determined at from (1) which is no longer valid but is calculated as follows. When the connection begins to plasticize, it is noted, as shown in Figure 4, which shows the theoretical appearance of the coefficient of friction between two surfaces in contact according to their relative speed V, that the coefficient of friction f (t) tends quickly to a constant value f _dynamic . This value can be calculated approximately by means of the relation (2), applied to the limit of the elastic domain, where the relation (1) is still valid for determining the instantaneous pulling force F (t). It is then sufficient to use the equation (2), reduced in this case to a simple linear equation, with the constant value found for _dynamic f for determining F (t) and the clamping stop when the set F _setpoint is reached the pulling force.

Thus, the clamping force can be achieved both in the elastic domain that plastic and this in one step. Indeed, the processing means are programmed to detect in real time the transition from the elastic domain to the plastic domain and modify accordingly the calculation of the force as described above.

After tightening, a certain amount of information, given in Table 1 below, is available. They are displayed on the display device 5. Table 1: Final characteristics of the tightening (C, θ, F) _tightening Characterization of friction f _static and _dynamic f Laminating screws • clamping in the field of elastic or plastic deformations • in the case of clamping in the field of plastic deformations: (C, θ, F) plasticization Traceability of the tightening C (t), θ (t), F (t), f (t)

The tightening wrench according to the invention also has the advantage of being able to resume an interrupted clamping before having reached the setpoint value, contrary to the conventional tightening torque (trigger key for example). Indeed, in the case of torque tightening with a torque wrench of the prior art, if the tightening was interrupted before its term, it is no longer possible to achieve the desired effort because, as shown Figure 4, when you want to resume tightening, the coefficient of friction is significantly higher than before interruption. It is therefore necessary to apply a tightening torque greater than that specified so that the force in the threaded element can grow again. With the tightening wrench according to the invention, this situation is automatically detected and managed thanks to the instantaneous measurements made on the torque C (t) and the rotation angle θ (t ) on the one hand, and the parameters, in particular the coefficient of friction, calculated according to equations (1) and (2) on the other hand.

FIG. 5 illustrates an example of resumption of clamping interrupted with the key according to the invention. In the figure, point A indicates the moment when the tightening is interrupted before reaching the setpoint, ie at the value F _stopinterm <F _setpoint . The means for processing the key detect that the clamping is interrupted because F _stopinterm <F is _set while the rotation angle θ (t) no longer changes. The intermediate value F _stopinterm is stored. At this time, we can remove the socket and do any kind of control operations on the equipment. When the tightening resumes, the processing means detect it by the information given by the torque C (t) which is changing again. The processing means detect the moment when the rotation angle θ (t) starts to increase and, as soon as it is the case, calculate the coefficient of friction f (t) whose evolution is represented by the curves in lines. discontinuous f _static 'and f _dynamic '. Thus, the tightening will be completed when the value of the measured effort ΔF (t), added to the stored value F _stopinterm when the clamping has been interrupted, reaches the setpoint, or when: $${\mathit{F}}_{\mathit{arrëtinterm}}+\mathrm{.DELTA.F}\left(\mathrm{t}\right)={\mathit{F}}_{\mathit{order}}$$

The curves in Figure 5 show that, in the case of interrupted tightening, more torque must be given than in the case of continuous tightening. The procedure described above makes it possible to take into account the physical reality, namely that the coefficient of friction may differ after the interruption of the clamping (adaptation of the surface states).

The use of the wrench of the present invention is not limited to the tightening of bolts. For example, the key can be used for tightening screws, plugs, unions and couplings as illustrated in Figures 6 to 8. As in Figure 2, the parts that are rotated during tightening are shown in solid lines while fixed parts are represented in broken lines.

FIG. 6 illustrates the configuration used for tightening a screw or plug 221 in order to assemble a first part 230 with a second piece 231 threaded to receive the threaded portion 221A of the screw. The tightening is performed with a key 200 similar to the key 100 of Figure 2. The angle of rotation is measured by a measuring device 210 which comprises a clamping sleeve 212 cooperating with the head 221B of the screw. The measuring device 210 measures the differential rotation between the bushing 212 and the first part 230 by means of a spring 213 disposed around the outer periphery of the bushing, a Teflon® tube 211 provided with a non-slip ring 214, being interposed between the spring 213 and the upper surface of the first piece 230.

FIG. 7 shows the tightening of a union 330 on an implantation element 331 with the interposition of a V-shaped seal type seal 332. In this configuration, the angle of rotation measuring device 310 comprises a clamping sleeve 312 with a spring 313, a Teflon® tube 311 and, optionally a slip ring 314, for measuring the differential rotation between the bushing and the implantation member 331.

Finally, FIG. 8 shows the tightening of a conical bearing connection formed of two pieces of tubing 430 and 431 assembled by a nut ring 432. In this example of application of the key according to the invention, the measuring device of FIG. the angle 410 always formed of a clamping sleeve 412, a spring 413, a tube 411 and a non-slip ring 414, measures the differential rotation between the sleeve and a clamping wrench 414 used to maintain in position the tubing piece 431.

The tightening operation described above in the particular case of the bolts force-tightening can easily be generalized to the other configurations described in relation with FIGS. 6 to 8. To do this, it suffices for this purpose to adapt the parameter length L to each of these configurations. As illustrated in FIGS. 2, 6 and 7, the parameter L represents the length of the part of the threaded element which is not in cooperation screw / nut, the nut can be a part as in Figure 6.

The above-mentioned diagrams for the various possible clamping configurations use rotation angle measuring systems using springs. Other means are possible, such as an optical measurement that replaces both the spring and the support sleeve.

The tightening wrench and its measuring and control means can also be used for other tightening methods such as torque, angle, torque and then angle (or vice versa), torque with control of the angle (or vice versa).

In the case of torque tightening, the tightening is carried out in the same way as with a conventional electronic key. It suffices to introduce on the key the target torque C _setpoint (Figure 1) and then tighten until a sound and / or light signal announces the obtaining of the imposed torque. The specific instrumentation of the sockets is not used in this type of clamping. In the case of angle tightening, the tightening is carried out according to the same principle as that of torque tightening. It suffices to indicate on the key the target tightening angle θ _setpoint and then tighten until an audible and / or luminous signal announces obtaining the imposed clamping angle.

In the case of tightening torque then angle (or vice versa), it is necessary to apply successively the above procedures relating to torque tightening and tightening at the corner (or vice versa). In the case of torque tightening with angle control (or vice versa), this new type of key is used to check the angle of rotation of the threaded element after application of the specified tightening torque. The opposite is also possible: tightening at the angle up to an imposed value, then control of the torque. In all cases, the value of the resulting traction force F is available at the end of clamping which allows to control the quality of the latter.

Whatever the use made of this new type of key, the coefficient of friction determined during tightening is provided, which is additional information as to the quality of the tightening performed.

Claims (14)

1. A wrench (100) comprising a head (101) suitable for co-operating with a screw fastener (122), means (2) for measuring the instantaneous applied torque, a head suitable for co-operating with a screw fastener, said head being fitted with means (3) for measuring the instantaneous angle of rotation, input means (4) for recording characteristics of the screw fastener and a setpoint value for tightening thereof, and processor means (1) for calculating the instantaneous traction force on the screw fastener as a function of the measured instantaneous values of torque and angle and as a function of the stored characteristics of the screw fastener,
   the wrench being characterised in that the processor means (1) further comprise software means for acting during the tightening operation to detect automatically the transition from the elastic range to the plastic range and to calculate the instantaneous traction force on the screw fastener as a function of the result of detecting the tightening range.
2. A wrench according to claim 1, characterised in that the processor means calculate the instantaneous force in real time so as to enable the screw fastener to be tightened in a single stage.
3. A wrench according to claim 1 or claim 2, characterised in that the processor means (1) further include software means for calculating the instantaneous coefficient of friction of the screw fastener during tightening, the instantaneous coefficient of friction (C(t)) being calculated by solving the following integral: $$\mathrm{C}\mathrm{\left(}\mathrm{t}\mathrm{\right)}\mathrm{=}{\mathrm{\int }}_{{\mathrm{t}}^{\mathrm{\prime }}\mathrm{=}\mathrm{0}}^{{\mathrm{t}}^{\mathrm{\prime }}\mathrm{=}\mathrm{t}}\mathrm{[}\mathrm{f}\mathrm{\left(}{\mathrm{t}}^{\mathrm{\prime }}\mathrm{\right)}\mathrm{\cdot }\frac{{\mathrm{D}}_{\mathrm{t}}}{\mathrm{2}}\mathrm{+}\frac{{\mathrm{d}}_{\mathrm{2}}}{\mathrm{2}}\mathrm{\cdot }\frac{{\mathrm{K}}^{\mathrm{\prime }}\tan \mathit{\alpha }\mathrm{+}\mathrm{f}\mathrm{\left(}{\mathrm{t}}^{\mathrm{\prime }}\mathrm{\right)}\mathrm{.}\cos \mathrm{\left(}\mathit{\alpha }\mathrm{\right)}}{{\mathrm{K}}^{\mathrm{\prime }}\mathrm{-}\mathrm{f}\mathrm{\left(}{\mathrm{t}}^{\mathrm{\prime }}\mathrm{\right)}\mathrm{.}\sin \mathit{\alpha }}\mathrm{]}\mathrm{dF}\mathrm{\left(}{\mathrm{t}}^{\mathrm{\prime }}\mathrm{\right)}$$

   

   
   where: $$\{\begin{array}{l}{\mathrm{d}}_2=\mathrm{d\hspace{1em}}\frac{3}{8}\cdot \sqrt{3.\mathrm{p}}\\ \tan \mathit{\alpha }=\frac{\mathrm{p}}{\mathit{\pi }\mathrm{.}{\mathrm{d}}_2}\\ {\mathrm{K}}^{\prime }=\frac{1}{\sqrt{1+{\tan }^2\mathit{\alpha }+{\tan }^2\mathit{\beta }}}\end{array}$$

   

   
   and:

   D_t: equivalent diameter of contact between the washer and the head of the bolt;

   d: thread diameter;

   α: helix angle of the fastener thread;

   d₂: theoretical diameter of contact between threads (on the flanks of the thread);

   β: half-angle of the thread of the fastener (30° for ISO M thread).
4. A wrench according to claim 3, characterised in that it includes means for detecting anomalies such as the connection binding as a function of the measured value for the coefficient of friction.
5. A wrench according to any one of claims 1 to 4,characterised in that the means for measuring the instantaneous angle of rotation comprise a socket (112) suitable for co-operating with the screw fastener, a bearing element (111) made of a material having a low coefficient of friction, and a spring (113) interposed between the socket and the bearing element, the end of the bearing element for coming into contact with the screw fastener being provided with an element having a high coefficient of friction (114).
6. A wrench according to any one of claims 1 to 5, characterised in that the processor means (1) include software means for restarting tightening that has been interrupted prior to reaching the setpoint value.
7. A wrench according to any one of claims 1 to 6, characterised in that it further includes storage means and a display device (5) for storing and displaying information relating to tightening and available at the end of the tightening operation.
8. A wrench according to claim 7, characterised in that the information relating to tightening comprises in particular the torque (C(t)) and angle of rotation (θ(t)) values measured during tightening, the traction force (F(t)) calculated during tightening, the static and dynamic coefficients of friction (f_static, f_dynamic) calculated during tightening, as well as the tightening range with information (C, θ, F)_plastic in the event of the screw fastener being subjected to plastic deformation.
9. A wrench according to claim 7, characterised in that the information relating to tightening includes how the calculated coefficient of friction varied as a function of speed and of time.
10. A wrench according to claim 7, characterised in that the information relating to tightening includes the calculated difference between the static and dynamic coefficients of friction.
11. A wrench according to any one of claims 1 to 10, characterised in that the setpoint value corresponds to a predetermined traction force, and that the wrench includes warning means operated by the processor means when the calculated force value reaches the setpoint value.
12. A wrench according to any one of claims 1 to 10, characterised in that the setpoint value corresponds to a predetermined tightening torque, and that the wrench includes warning means operated by the processor means when the measured torque value reaches the setpoint value.
13. A wrench according to any one of claims 1 to 10, characterised in that the setpoint value corresponds to a predetermined tightening angle, and that the wrench includes warning means operated by the processor means when the measured value for the angle of rotation reaches the setpoint value.
14. A wrench according to any one of claims 1 to 13, characterised in that said wrench is a manual wrench, the means (2) for measuring the instantaneous applied torque, the input means (4), and the processor means (1) being included in a handle (102) to enable an operator to perform tightening manually.

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