EP1000710B1 - Method of mesuring and/or controlling in a fastening device including a hydropneumatic impulse screw driver - Google Patents

Description

The present invention relates to hydropneumatic screwdrivers of the pounding type. In the present context, the term "hammering" designates the operation of the screwdrivers whose driving shaft does not rotate at a constant speed, but in successive successive angular steps, which applies to the object to be tightened (screws, nut, bolt, etc.) jerky tightening torques.

Such tools are used in assembly shops to perform, usually manually, all kinds of assembly operations.

Different types of screwdriver are known, for example, from publications EP-A-0911119; DE-A-4243069 and DE-A-4429282.

Hammering screwdrivers are newly introduced equipment on the market. Although they offer significant advantages in particular by the absence of reaction on the hand of the operator during tightening and by the shortening of the time required to tighten an assembly, they have a significant disadvantage. Indeed, so far, it has not been possible to accurately measure the tightening torque present in the assembly after the clamping operation. However, this data is often essential to guarantee the quality of a finished product or the safety criteria to which a finished product must satisfy.

One example, among many others, an assembly requiring the exact knowledge of the tightening torque is the attachment of a peduncle of a seat belt to the floor of a motor vehicle. Because of the difficulties encountered in measuring the tightening torque of the hammer screwdrivers, such an operation is still being carried out using conventional screwdrivers with continuous rotation whose operation is slower but whose torque finally obtained may be duly verified.

Moreover, because of the specificity of operation of the hammer screwdrivers, it has not been possible to combine them with torque measuring apparatuses currently used with the screwdrivers with continuous rotation.

It follows that we hesitate to use the screwing hammers yet very fast, when the assembly must meet specific criteria of quality and safety, the lack of knowledge of the tightening torque applied may lead, in an assembly that the it is believed to have tightened to the nominal value, either a lack of sufficient clamping or an excess of clamping resulting in exceeding the elastic limit of a screw for example.

To understand the phenomena that take place during the operation of a hammer screwdriver of the type described above, the Applicant has carried out, in a test assembly, the reading of several curves, the diagrams of Figures 2 to 6 of the drawings. annexed are representations.

Figure 1A of the accompanying drawings shows in sectional view the test assembly used by the Applicant in these investigations.

This test assembly had two pieces P1 and P2 to be clamped against each other with a screw V. For example, the piece P1 was a relatively non-rigid plastic plate and the piece P2 was a metal sheet. The screw passed through a smooth hole T1 of the workpiece P1 and was screwed into a threaded hole T2 of the other workpiece. Furthermore, under the head of the screw V was placed a stress sensor C which measured the stress exerted by the head of the screw V on the face of the part P1 during the various phases of the clamping operation using a hammer screwdriver. The pace of the The stress as a function of the time recorded by this sensor C is shown by the curves A of FIGS. 2 and 3.

Furthermore, a torque transducer interposed between the screwdriver and the screw was used to plot the torque curves B as a function of time in FIGS. 2 and 3, to examine the behavior of the torque applied to the head of the screw V.

Thus, FIG. 2 shows these curves for a hammer screwing machine with automatic cut-off of its pneumatic supply, this cut occurring when the value of the tightening torque chosen by the operator is reached during a clamping operation and FIG. analogous, but for a pounding screwdriver without automatic shut off pneumatic supply.

It will also be noted that, with respect to FIG. 2, the polarities of the measurement signals represented in FIG. 3 are reversed, which is only a simple question of connecting the sensors and does not fundamentally change the general appearance of the signals. curved curves.

By first examining FIG. 2, it can be seen that, at the beginning of the tightening process, the screw V is rotated during a time t ₀ , without any significant resistance torque remaining to the screwdriver. This will tighten the screw step by step until it begins to resist resistance to its own rotation. The two pieces P1 and P2 are then applied to each other without constraint.

However, after the completion of the duration t ₀ , it can be seen that the stress in the assembly begins to increase in stages during successive cycles t ₁ to t _n-1 which correspond to as many hammering steps of the screwdriver.

It is also seen that at each stroke of the screwdriver, the tightening torque rises abruptly, the curve B representative of the tightening torque thus comprising several "peaks" whose vertices are generally higher and higher. This is explained by the fact that the assembly is more and more under stress and that the screw V opposes more and more resistance to its own rotation. When a torque peak reaches for the first time the value at which the screwdriver is set, it cuts off its pneumatic supply (in Figure 2 at the end of the cycle t _n-1 ). Therefore, the value of the applied torque drops to zero, while the constraint in the assembly reaches its maximum value, meaning in principle that all the sets of the assembly and all the deformations of the parts P1 and P2 have been made up.

The test illustrated in Figure 2 shows approximately steady growth of the peaks representing the tightening torque applied at the beginning of each pounding cycle. However, it turns out that such a regular growth is not, and by far, the general case, the highest peak peaks can occur while the desired nominal stress in the assembly is not yet reached . The diagram shown in FIG. 3 shows the stress and torque curves of such a case.

Here, the beginning of the tightening (period to) also corresponds to a constant overall rate (curve A) of the stress while the pieces P1 and P2 are brought in support on one another. Then, during the pounding cycles t ₁ to t _n-1 , the stress increases steadily in the assembly until reaching a constant value which reflects the completion of the tightening of the assembly. However, we see that in this case, the peaks of the curve 3 representative of the pair of tightening applied at each stroke of the screwdriver vary considerably and irregularly from one cycle to the next cycle, so that from the peak information provided by the torque sensor, it is impossible to deduce, if the assembly has been tight at the fair value of stress or not. We see in particular that the peak at the beginning of the cycle t _n-2 is much higher than that of the cycles t _n-1 and t _n , whereas the curve A shows that the definitive stress is installed in the assembly only at the end of the period t _n .

This phenomenon of irregularity of the torque applied to the screw V comes from several factors which are difficult to control and vary considerably, particularly as a function of the surface condition of the parts of the assembly (presence of grease or dirt on the parts), the number of superimposed components of the assembly, more or less compressible materials of parts etc. It should be noted that the irregularities of the peaks can occur both for a screwdriver with automatic power failure and for a screwdriver without this cut.

As a result of these findings, a conventional pound-type hydropneumatic screwdriver can not be used, if it is necessary to precisely guarantee a prescribed value of stress in a screw connection.

It will also be observed that a strain sensor such as the sensor C of FIG. 1A can obviously not be installed in practice in an assembly (it could no longer be removed) so that in fact the information concerning the stress is not available for proper control of the tightening process.

From these observations, the Claimant continued its investigations by detailing in time each peak of the diagrams such as those shown in Figures 2 and 3.

Thus, FIG. 4 represents, on a time scale of significantly greater resolution, the shape of one of the peaks of the diagrams of FIGS. 2 and 3, such a peak corresponding to a shot of the screwdriver, it being understood that all the peaks generally have a roughly similar profile.

It can be seen that each peak is preceded by a stopping time (phase P1) of the screwdriver during which the torque is substantially zero, followed by a phase P2 of sudden rise towards an absolute maximum M1 (which is in fact the only one). maximum value visible at each peak in Figures 2 and 3).

This relatively large torque value is explained by the fact that since the previous pounding cycle, the screw V remains temporarily locked in rotation, and to "take off" it is necessary to overcome a relatively large resisting torque, before the screw can again turn. In fact, during this "peeling" phase P2, the screw is deformed by twisting about its axis until, abruptly, the friction forces on the surfaces in contact are exceeded. But this actually means that the emergence of this maximum torque M1, does not coincide in time with the installation of an increase in stress in the assembly.

The beginning of the following phase P3 shows that the screwdriver has overcome the resistance opposing the rotation of the screw V, the supplied torque then evolving towards a relative minimum value M2, to immediately go back to a relative maximum M3, the transition corresponding to a rotation of the screw against the friction forces generated on its threads and those of the hole T2. As a result, the screw progresses axially in this hole and the assembly is tightened to a new stress value (actually installed). In the case shown, this clamping is done in two steps (relative minimum M4 and relative maximum M5) but this is not systematic for all cases.

Phase P4 begins with the sudden release of the force provided by the screwdriver (the step is completed) so that the applied torque decreases to zero.

Then, a new pounding cycle begins with the creation of a torque profile that may have the same overall shape as the previous cycle, but with different maximum and minimum values, precisely because of all the factors. of uncertainty listed above.

Thus, for example, a following cycle of a tightening process may have a shape such as that shown in FIG. 5 in which the directions of the variations of the tightening torque are approximately similar, while the values of the cusp points of the curve are all different. Thus, the torque M1a necessary to "take off" the screw by applying a twist to it, is here a relative maximum, less than the maximum absolute torque M4a that will increase the stress installed in the assembly during this pounding cycle.

It can therefore be seen that it is extremely uncertain to take, in each cycle of the screwdriver, as a torque value that is significant for the stress actually installed in the assembly by this operating cycle, the absolute maximum value of the torque and, a fortiori, stop the tightening when, at a given moment, a value of the torque measured by the torque sensor corresponds to the value at which the screwdriver was previously set.

However, the study of the curves of FIGS. 2 and 3 has also revealed that, when the assembly is completely tightened by catching all the games and absorbing all the deformations of the pieces P1 and P2, a change in the shape occurs. the torque peak now applied, compared to that of all previous peaks.

This modification (see FIG. 6) seems to be due to the fact that the tightening torque applied by the screwdriver only succeeds in deforming the screw in torsion without being able to turn it further so that the curve has only one maximum Mn. In other words, in this assembly situation, the torque increases abruptly, until the screw is deformed and then drops back to zero at the end of the corresponding pounding cycle.

The present invention proposes to exploit this knowledge concerning the assembly process carried out with the aid of a hydro-pneumatic hammering screwdriver and it is therefore intended to provide a method for measuring the torque installed using a sensor interposed between the screwdriver and the assembly is to control a hydropneumatic hammer screwdriver to stop the screwing at the moment when the desired nominal stress is installed in a screw connection. The invention also aims to provide equipment for implementing this measurement and / or control method.

• une visseuse à martèlement hydropneumatique comportant un arbre d'entraînement qui, par l'intermédiaire d'un embout de vissage, peut appliquer un couple de serrage à des moyens de vissage par lesquels un assemblage doit être serré, la visseuse comprenant également un capteur de couple qui est associé audit arbre d'entraînement et qui délivre un signal de mesure représentant le couple instantané transmis par ledit embout sur lesdits moyens de vissage, ce signal de mesure comprenant une succession de cycles, respectivement représentatifs de l'évolution du couple de serrage pendant les coups successifs appliqués par la visseuse sur lesdits moyens de vissage, et
• des moyens de commande pour arrêter la visseuse,

ce procédé étant caractérisé en ce qu'il consiste à:

• détecter au moins un maximum dans chacun desdits cycles dudit signal; et
• arrêter la visseuse dès qu'un cycle ne présente qu'un seul maximum.

It therefore relates to a method for measuring and / or controlling a screwing equipment comprising

• a hydro-pneumatic hammer driver having a drive shaft which, by means of a screwdriver bit, can apply a tightening torque to screw means by which an assembly is to be tightened, the screwdriver also comprising a screwdriver couple who is associated with said tree drive and which delivers a measurement signal representing the instantaneous torque transmitted by said tip to said screwing means, this measurement signal comprising a succession of cycles respectively representative of the evolution of the tightening torque during the successive shots applied by the screwdriver on said screwing means, and
• control means for stopping the screwdriver,

this method being characterized in that it consists in:

• detecting at least a maximum in each of said cycles of said signal; and
• stop the screwdriver as soon as a cycle has only one maximum.

Thus, the screwing process can be stopped when it is certain that the assembly is completely tightened and that no backlash of play or elastic deformation in the assembly is still possible. The tightening operation will therefore practically lead to to install in the assembly the maximum stress value that can be obtained without this stress value being available or being measured.

According to a first variant of the method of the invention, it also consists in detecting in each of said cycles preceding said cycle having only one maximum of said measurement signal, at least one other maximum, to memorize the value of this other maximum during the next cycle of this signal and displaying said value if, during the current cycle of said signal, only one maximum is detected.

In this variant, an operator can easily cause the stopping of the screwdriver by observing the display by manual cut-off of the power supply thereof.

However, according to another advantageous variant of the invention, the stopping of said screwdriver is caused automatically by cutting off its power supply, by means of a generated stop signal, following the detection of a single maximum during the current cycle of said measurement signal.

The invention also relates to a screwing equipment controlled by the method as defined above, this equipment comprising
a hydro-pneumatic hammer driver having a drive shaft which, by means of a screwdriver bit, can apply a tightening torque to screw means by which an assembly is to be tightened, the screwdriver also comprising a screwdriver torque which is associated with said drive shaft and which delivers a measurement signal representing the instantaneous torque transmitted by said tip on said screwing means, this measurement signal comprising a succession of cycles respectively representative of the evolution of the tightening torque during the successive strokes applied by the screwdriver on said screwing means, and
control means for stopping the screwdriver,
characterized in that said control means also comprises means for analyzing each of the cycles of said measurement signal, said analysis means being arranged to supply the value of the torque applied to the assembly, as soon as a cycle of said signal measurement has only one maximum.

• lesdits moyens de commande comprennent des moyens de coupure manuels de ladite alimentation et des moyens pour afficher ladite valeur
• lesdits moyens de commande comprennent des moyens connectés auxdits moyens d'analyse et capables de provoquer l'arrêt automatique de la visseuse.

According to other characteristics of this equipment:

• said control means comprise means for manually cutting said supply and means for displaying said value
• said control means comprise means connected to said analysis means and capable of causing the automatic shutdown of the screwdriver.

• la figure 1 est un schéma très simplifié d'une visseuse à martèlement et de son appareillage de commande, ce dernier étant apte à mettre en oeuvre le procédé de mesure et/ou de commande selon l'invention;
• la figure 1A est une vue en coupe d'un assemblage d'essai utilisé par la demanderesse ;
• la figure 2 est un diagramme en fonction du temps illustrant le fonctionnement d'une visseuse à martèlement dont l'alimentation pneumatique est coupée lorsque la visseuse fournit un couple de serrage égal à celui affiché par l'opérateur;
• la figure 3 est un diagramme analogue à celui de la figure 2, mais portant sur une visseuse dont l'alimentation pneumatique reste appliquée, même lorsque le couple de serrage souhaité est atteint;
• les figures 4 à 6 représentent, à une échelle temporelle très agrandie par rapport aux figures 2 et 3, la forme d'une partie de l'une des courbes du diagramme de ces figures, pour différentes phases de fonctionnement de la visseuse;
• la figure 7 montre un organigramme simplifié du procédé mis en oeuvre selon l'invention, dans l'appareillage représenté à la figure 1.

Other features and advantages of the invention will become apparent from the following description given solely by way of example and with reference to the appended drawings in which:

• Figure 1 is a very simplified diagram of a hammer screwdriver and its control apparatus, the latter being able to implement the measuring method and / or control according to the invention;
• Figure 1A is a sectional view of a test assembly used by the Applicant;
• FIG. 2 is a time diagram illustrating the operation of a pusher screwdriver whose pneumatic supply is cut off when the screwdriver provides a torque equal to that displayed by the operator;
• Figure 3 is a diagram similar to that of Figure 2, but on a screwdriver whose pneumatic supply remains applied, even when the desired torque is reached;
• Figures 4 to 6 show, on a time scale greatly enlarged with respect to Figures 2 and 3, the shape of a portion of one of the curves of the diagram of these figures, for different phases of operation of the screwdriver;
• FIG. 7 shows a simplified flowchart of the method implemented according to the invention, in the apparatus shown in FIG.

FIG. 1 very schematically represents a hammer driver 1 equipped with an electronic apparatus 2, the assembly being designed for implementing the method according to the invention.

The screwdriver 1 essentially comprises a body 3 having an anatomical shape so that it can easily be manipulated by hand. This body 3 encloses the mechanical members known per se of the screwdriver, among which only drive shaft 4 is shown, a torque sensor 5 and a coupling end 6 intended to cap the head of a screwdriver. screw, a nut, or other similar screwable member, when tightening an assembly. Also shown schematically a connector 7 for a pneumatic supply of the screwdriver and an actuating button 8. The structure of the screwdriver 1 itself not forming part of the invention, it will not be further described. It suffices to note that the hammering consists in applying the clamping force during cycles of rotation of the endpiece 6 around its axis, the cycles succeeding one another very quickly.

Screwdrivers of this type are marketed for example by ATLAS COPCO S-10523, Sweden or by DGD GmbH, Postfach 30, D 73461 WESTHAUSEN / Würth, Germany.

The sensor 5 can be made using strain gauges placed on the drive shaft 4 of the screwdriver and appropriately connected to provide an electrical voltage across the sensor representative of the torque applied to the tip. 6.

The terminals of the sensor 5 are connected to the electronic equipment 2 which comprises an analog filter 9 to clear the signal from the sensor, an amplifier 10 connected to the filter 9 followed by an analog / digital converter 11, a filter 12 of a processing module 13 and a display 14. The processing module 13 comprises a microprocessor (not shown) capable of executing a program whose essential steps are illustrated in FIG. 7 and which will be described by FIG. the following. The processing module 13 may possibly generate a signal for cutting off the pneumatic supply of the screwdriver 1, this signal then being able to transit on a line 15.

FIG. 7 represents a flowchart that can be executed in the processing module 13 of FIG. 1 for carrying out the method according to the invention. This flow chart takes place during each tightening process. Thus, the program illustrated by the flowchart of Figure 7 is triggered in E1 as a new tightening process begins. The operation E2 consists in searching for a first maximum value M1 (FIG. 4) of the torque value from the signal coming from the sensor 5, this signal being shaped, amplified and digitized in the filtering, amplifying stages. and conversion 9 to 12 of Figure 1.

The operation E3 consists in detecting in the signal whether the maximum value M1 is followed by a relative minimum M2 corresponding to a trough of the torque profile. A test is then performed in step E4 to determine if the relative minimum point M2 is followed by a relative maximum point (search for the point M3) corresponding to a second peak of the torque profile.

If at this stage, there is no second peak, it means that we are in the case of Figure 6 and the final voltage value is immediately obtained in the assembly. Practically, this case can occur if the assembly comprises few parts and / or if it is formed of parts made of particularly resistant materials.

In this case, the program proceeds to an evaluation step E5 of the value of the tightening torque which is the one corresponding to the maximum observed. This value is then displayed during a step E6 on the dial of the screwdriver. The operator stops the tightening process.

If, on the contrary, the step E4 notes the presence of a second peak, a test is performed during the step E7 to see if a new tightening cycle has begun. If it is not the case, it is because the screwdriver has been stopped by the operator and in this case the value of the second or the third peak memorized during the previous cycle is calculated in E8 and the corresponding value is displayed by step E6.

If, on the contrary, during the test of step E7, it turns out that a new pounding cycle has begun, the search is again made for an absolute maximum in E9 followed by the search for a new minimum. relative to E10, these steps being similar to steps E2 and E3.

After step E10, a test is performed at E11 to see if the first peak is followed by a second peak. If the response is negative, the value of the second or third peak of the torque profile of the preceding cycle is calculated at E12, which then corresponds to the nominal value of the torque applied to the assembly. This value stored during the previous cycle is displayed by step E6 during the current cycle and the operator can stop the screwdriver.

Otherwise, the program waits for the next pounding cycle by testing step E13. If there is a cycle following the loop is again traversed by the steps E9, E10 and E11.

If, on the other hand, the test of step E13 proves to be negative, it is because the assembly is tight and the value of the second or third peak of the torque profile of the previous cycle is displayed during step E12.

It should be noted that, according to an advantageous variant of the invention, the display step E6 can be performed at the same time as a step E14 of controlling the automatic cutting of the screwdriver via the order 15. It should be noted that this automatic cut-off will be carried out according to the actual tightening torque applied to the assembly to install the required tension.

Claims (6)

1. A process for measuring and/or controling a screwing apparatus comprising

   - a hydropneumatic hammering screwing device (1) comprising a drive shaft (4) which, by way of a screwing end portion (6), can apply a tightening torque to screwing means (V, T2) by which an assembly is to be tightened, the screwing device also comprising a torque sensor (5) which is associated with said drive shaft (4) and which delivers a measurement signal representing the instantenous torque transmitted by said end portion (6) to said screwing means (V, T2), said measurement signal comprising a succession of cycles which are respectively representative of the variation in the tightening torque during the successive blows applied by the screwing device (1) to said screwing means, and

   - control means (8) for stopping the screwing device (1),

   
   said process being characterised in that it comprises:

   - detecting at least one (M1, M3, M5) in each of said cycles of said signal; and

   - stopping the screwing device (1) as soon as a cycle has only one single maximum (Mn).
2. A process according to claim 1 characterised in that it comprises:

   - detecting in each of said cycles preceding said cycle which has only one single maximum of said measurement signal, at least one other maximum (M3, M5),

   - storing the value of said other maximum in the course of the following cycle of said signal, and

   - displaying said value if, during the onging cycle of said signal a single maximum (Mn) is detected.
3. A process according to the either one of claim 1 and 2 characterised in that the stoppage of the screwing device (1) is caused automatically by cutting off its supply (7) by means of a stoppage signal (15) produced following detection of a single maximum (Mn) during the ongoing cycle of said measurement signal.
4. A screwing apparatus controlled by the process according to any one of claims 1 to 3 comprising a hydropneumatic hammering screwing device (1) comprising a drive shaft (4) which, by way of a screwing end portion (6), can apply a tightening torque to screwing means (V, T2), by which an assembly is to be tightened, the screwing device (1) also comprising a torque sensor (5) which is associated with said drive shaft (4) and which delivers a measurement signal representing the instantaneous torque transmitted by said end (6) to said screwing means (V, T2), said measurement signal comprising a succession of cycles which are respectively representative of the variation in the tightening torque during the successive blows applied by the screwing device (1) to said screwing means, and control means (8) for stopping the screwing device (1),
   characterised in that said control means also comprise analysis means (9 to 13) for each of the cycles of said measurement signal, said analysis means being arranged to supply the value of the torque applied to the assembly as soon as a cycle of said measurement signal has only one single maximum (Mn).
5. Apparatus according to claim 4 for carrying out the process according to claim 2 characterised in that said control means comprise manual cut-off means (8) for said supply and means (14) for displaying said value.
6. Apparatus according to claim 4 for carrying out the process according to claim 3 characterised in that said control means comprise means (15) connected to said analysis means and capable of causing automatic stoppage of the screwing device (1).

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