DE19944717A1 - Method for operating a screwing device - Google Patents

Abstract

The invention relates to a method for operating a screwing device for producing a defined screw joint (13, 15), by which means at least two parts (11, 12) are pressed against each other with a predetermined clamping force. The method comprises the following steps: detecting the acoustic emission present in a screw and/or the parts (11, 12) to be clamped during at least one reference screwing process and producing a corresponding electrical or optical signal; extracting at least two characteristics from said electrical or optical signal using mathematical methods; determining which characteristic has the curve that best correlates with the clamping force; establishing the characteristic curve between the clamping force and the determined characteristic; configuring a signal or data processing device in such a way that the determined characteristic can be calculated directly from the electrical or optical signal; and controlling and/or monitoring and/or process-evaluating the screwing process in dependence on the established characteristic curve and the signal provided by the signal or data processing device.

Description

The present invention relates to a method for operating a Screwing device for establishing a defined screw connection, via the at least two components with a predetermined clamping force be pressed together.

Electronically controlled are often used in industrial production Tightening systems used that have a drive unit and a factory tool spindle with a screwing tool a screw with a vorbe screwed in torque to connect to each other Press parts together with a certain clamping force. That power is also known as the pre-tensioning force and arises from the elastic Change in length of the screw shaft. In many use cases it is necessary to adjust the clamping force of the screw connection as precisely as possible set a predetermined value. This requires while of the screwing process to determine the clamping force of the screw connection teln.

It is known to measure the preload indirectly by measuring the Determine torque during the screwing process, taking off the torque introduced into the screw connection to the front tension of the screw connection is closed. With this indirect th determination of the biasing force, however, the problem arises that when  Tightening a screw only partially applies the applied torque the change in length of the screw and thus the generation of the front clamping force, while the other part of the torque is caused by the Friction of screw thread and screw head is absorbed. However, since these coefficients of friction are subject to strong fluctuations the torque only conditionally to produce a reproducible suitable for tension.

Another known possibility for determining the prestressing force is in the published patent application DE 40 17 726 A1, in which by means of Ultra sound the change in length and thus the preload of a screw is measured. To do this, a piezo element that was previously on the Screw was applied, an ultrasonic pulse into the screw which is generated by an external source. The ultrasound waves are reflected from the end of the screw, and by means of the piezo Elements can be the transit time of the ultrasonic waves in the screw be true. Due to the duration, it is possible to determine the length of the Determine screw that is essentially proportional to the clamping force is. The determination of the change in length of the screw using Ultra However, sound has the disadvantage that the sound introduction area Chen and the reflection surfaces are formed and closed with high precision which must be equipped with an ultrasonic sensor. The ferti Delivery costs for such special screws are therefore proportional high.

There is therefore a need for a method for direct determination to create the clamping force on screw connections that the above be overcomes the written problems.

The object of the invention is  in providing a method of operating a screw device len with which the clamping force (pretensioning force) of a screw connection determined and set reliably and reproducibly as well as the Screwing process can be monitored.

The task is there in principle with a method according to claim 1 solved by that using a screw device a defined Screw connection is made, via the at least two components a predetermined clamping force are pressed together, the acoustic emissions during at least one reference Screwing process in a screw and / or to be braced Components arise, recorded and in a corresponding electrical or optical signal to be converted from the clamping force of the Determine screw connection directly.

The process according to the invention is characterized in detail by the following process steps:

• - Extraction of at least two features from the electrical or optical signal using mathematical methods,
• - Determine the feature whose course is best with the Clamping force of the screw connection correlated,
• - Set up the characteristic between the clamping force and the ermit feature,
• - Configuration of a signal or data processing device such that the determined feature directly from the electrical or optical signal is predictable, and  
• - Control and / or monitoring and / or process evaluation of the Tightening process depending on the determined characteristic and that supplied by the signal or data processing device Signal.

By changing the length of the screw during screwing gangs occurs due to deformation processes in the screw and / or their surroundings an acoustic emission. With this acousti a measurement is available that gives a direct return conclude on the load in the screw and thus on the clamping force prevailing between the two components.

In the method according to the invention, this effect is advantageous Exploited by the acoustic emission one with the Clamping force is closely correlated characteristic obtained by Reibef in the thread or on the screw head is independent and for control tion of the screwing process can be used. With that comes one Procedures are available with which the actual clamping force of a Screw in a screw connection directly and with high accuracy can be determined. The method according to the invention also has the Advantage that it is for conventional screws and screw connections can be applied without this undergoing a specific modification need to.

Advantageous developments of the method according to the invention are shown in the description and specified in the subclaims.  

In a particularly preferred embodiment of the method according to the invention

• - a frequency analysis of the he as part of the feature extraction generated electrical or optical signal,
• - Determines the frequency band in which the best correlation between the clamping force and the electrical or optical signal is present
• - The characteristic between the clamping force and that signal part that lies in the determined frequency band,
• - A band forming the signal or data processing device pass filter set according to the determined frequency band, and
• - The control and / or monitoring and / or process evaluation of the screwing process depending on the characteristic curve determined and the signal provided by the bandpass filter.

Because the acoustic emission depends on the application of the screw connection varies and is overlaid with a variety of noise, it is advantageous if the electrical or optical signal is not directly for the Control of a screwdriver is used, but if one Separation of useful part and interference signal takes place. For this purpose according to the latter process variant within the scope of a Pra Upstream calibration procedure by at least one ref renz or calibration screwing derived electrical or optical Si gnal be transformed into its frequency range, whereupon as Si signal characteristic that frequency band of the signal is determined that the has the best correlation to the clamping force generated. The following Screwing is then due to the bandpass filter provided only the signal component in the selected frequency band remains white  processed. In this way, interference can be greatly reduced den and it is in particular also possible for each individual The most suitable frequency band and thus the most effective Select interference suppression.

The signal processing can alternatively in the screwing tool or done externally. The preamplification is preferably already in the Screwing tool instead, because the electrical or optical signal is very small and is therefore susceptible to interference.

In a preferred development of the method according to the invention is the ge of the signal and data processing device currently delivered signal in an evaluation unit with that during the calibration process characteristic curve compared and based on the comparison result The current screwing process ends as soon as the screw connection the desired clamping force has been reached. In addition, the Screwing process controlled, evaluated and / or by the evaluation unit be documented.

The calibration method according to claim 1 is with a special measurement direction carried out so that the actual clamping force of a Screw connection together with that created during the screwing process the acoustic emission can be measured synchronously. During the Verification procedure the clamping force of the screw connection becomes the determin tion of the characteristic curve is preferably determined via a force sensor which arranged between the two components to be screwed together is not.  

Alternatively, it is also possible to simulate the characteristic curve by ver holding the components and / or the screw, by simulating the Screwing process, by finite element methods and / or by Determine boundary element methods.

Both in the calibration process and in the practical use of Screwing device can be used to record the acoustic emission a sampling frequency between 700 kHz and 1.3 MHz, preferably with a Sampling frequency of 1 MHz.

The invention can be realized particularly economically if the Fre frequency analysis of the electrical or optical signal using a fast Fourier transform is performed. The Fre determined quenzband in which the best correlation between the clamping force and the electrical or optical signal is preferably between rule 100 kHz and 450 kHz, the width of a frequency band be is preferably about 100 kHz.

In an advantageous development of the method according to the invention becomes the electrical or optical generated from the acoustic emission Signal during the calibration method according to the invention and / or wäh rend the practical use of the screwing device by means of a Ver intensified and / or processed by means of a preprocessing filter tet, preferably an effective value formation or an RMS signal formation (RMS: root mean square), d. H. the formation of the root mean square of the signal. The preprocessing filter is preferably in Dependence on the frequency band is set and can in particular Smooth the signal. The control of the screwing tool  then follows depending on the characteristic and the bandpass, Amplifier and / or signal supplied by the preprocessing filter.

In the calibration method according to the invention and / or during the practi The use of the screwing device can be from the bandpass, from Amplifier and / or signal supplied by the preprocessing filter Lich integrated, the integral formation only after a prep agreed offset begins. This offset can vary from screw to ver screw vary.

The integral calculation can depend on one for the respective Screwdriving characteristic quantity or depending on it start over time. Here, for. B. the torque with which the screwing device acts on the screw connection and determine the integral calculation depending on the additional torque is started (triggered). Then the Offset subtracted from the integral.

Depending on the Gra served the integral curve or from another additional measured variable respectively.

Preferably, the determined frequency band in which the best correlates tion between the clamping force and the electrical or optical signal is present, to the screwing device, in particular to the screwing mechanism witness the screwing device and there to adjust the Bandpass filter used. The determined characteristic curve can also be applied to the Screwing device, in particular to an outside of the screw mechanism Stuff arranged control unit of the screwing device transmitted and  be saved there. However, the control unit can alternatively also in the Screwing tool itself.

It is also possible to control the tightening operations of others Make measurement signals or measurement variables dependent, such as. B. the Torque, the angle of rotation, reaching the yield point or the Screw depth. If necessary, it is also possible to add more than two measured variables combine. Such combinations of several parameters can be used in particular for screw connections in which monitoring and evaluation based on specified quality criteria male is required.

In an alternative embodiment of the method according to the invention rens during the practical use of the screwing device determines the maximum of the electrical or optical signal that the Yield strength of the screw during the screwing process, and the Screwing process ended shortly after reaching the maximum. Since that Maximum in the sound signal during a tightening process of the yield point Screw corresponds, the screwing process is shortly after the maximum finished in order to achieve the maximum clamping force. For this process variant is not necessary, the above mentioned Determine characteristic. Furthermore, this method can also optionally without the feature extraction method described above or for frequency band determination and without the use of a bandpass filter apply.

In the following a screwing device and a device for Measurement of reference values of the clamping force with reference to the  attached drawings described to carry out the procedure rens are suitable according to the present invention. Show:

Figure 1 is a sectional view of a screwing device for performing the method according to the invention.

Fig. 2 is a sectional view of an apparatus for measurement of Re ference values of the clamping force for the implementation of the method according to the invention;

FIG. 3 shows two graphs each dung the time courses of the measured in a calibration operation of the clamping force and constitute Schraubverbin sion of the signal generated during the screwing electrical or optical signal of the acoustic Emis;

Fig. 4 is a diagram illustrating the time course of the root mean square value (RMS) of the acoustic signal for several frequency ranges between 100 kHz and 450 kHz and the time course of the measured clamping force; and

Fig. 5 shows two diagrams each showing the time profiles of the clamping force of the screw connection and the torque introduced into the screw connection and the time profiles of the RMS signal and the RMS integral.

As can be seen from the sectional view of a screwing device shown in FIG. 1, the screwing tool 1 comprises a motor-driven rotary drive shaft 2 , through which a tool tip designed as a screwdriver bit 3 is set into a rotary movement. The only torque thus generated management is initiated by the rotary drive shaft 2 through the screwdriver bit 3 in a screw head 8 of a screw 9, the case b screws into a component 10, and thereby the two members 10 a and 10 b together.

The screwdriver bit 3 is mounted in a receptacle 4 at the end of the rotary drive shaft 2 and is held in the receptacle 4 by a union nut 5 . The screwdriver bit 3 has at its end facing the screw 9 a shape of the force application feature of the screw head 8 accordingly. The other end of the bit 3 is equipped with a corresponding of the receptacle 4 in the rotary drive shaft 2 of force characteristic to the torque from the drive shaft 2 Drehan take.

The rotary drive shaft 2 contains a cavity 6 , which connects to the receptacle 4 of the screwdriver bit 3 in the rotary drive shaft 2 . In this cavity 6 , a sound sensor 7 is accommodated, which is in contact with the screwdriver bit 3 via a flat, preferably ground coupling surface and is thus acoustically coupled to the screwdriver bit 3 .

The acoustic emissions that occur when the screw connection is tightened are first transmitted via the screw head 8 to the screw bit 3 . Due to the torque applied by the screwing tool 1 and the contact pressure between the screwdriver bit 3 and the screw head 8, there is a high surface pressure between the surfaces, whereby the surfaces are coupled to one another in such a way that the acoustic emission from the screw head 8 is well transmitted to the screwdriver bit 3 .

The screwdriver bit 3 forwards the acoustic emissions to the sound sensor 7 . The sensor 7 is preferably a piezoelectric transducer and converts the acoustic emissions transmitted by the screwdriver bit 3 into electrical or optical signals. These electrical or optical signals are fed directly to an amplifier (not shown) via the shortest possible transmission line (not shown) and converted there into voltages that result in a transportable and further-processable electrical signal. From the amplifier, the signal is fed to a processing unit (not shown), through which a signal proportional to the clamping force is generated by the method according to the invention. After processing, the signal is forwarded to an evaluation unit, not shown in the drawing, which carries out the control of the screwing process according to the inventive method.

The screwing device shown in FIG. 1 is suitable both for carrying out the calibration method claimed in the context of the invention and for the production of screw connections controlled according to the invention in practical use.

In Fig. 2 a sectional view is shown of an apparatus solution for Mes suitable reference values of the clamping force by the inventive process. The measuring device shown is used to obtain reference values for the clamping force of a screw connection with which two components are pressed together. The measuring device comprises a lower component 11 mounted on a base plate 20 and an upper component 12 , which are connected to one another via a screw connection 13 , 14 , 15 and are pressed together.

The screw connection consists of a screw 13 , 14 which is screwed into a counter part 15 . The counter part is mounted in a recess in the lower component 11 , while the screw 13 rests with its screw head 14 on the upper component 12 . In this way, the screw connection 13 , 15 presses the two components 11 , 12 against one another, wherein between the components 11 , 12 force transducers 16 , 17 are arranged, which are the force with which the two components 11 , 12 are pressed against one another, and thus directly measure the clamping force of the screw connection 13 , 15 . In order to prevent lateral displacements of the upper component 12 relative to the lower component 11 , guide pins 18 , 19 are provided which are slidably mounted in corresponding bores in the two components 11 , 12 at least with respect to one of the two components 11 , 12 , around the components 11 , 12 during the Preßvor gear to align their movement.

Reference values for the clamping force are determined by producing the screw connection 13 , 15 using a screwing tool, for example of the type shown in FIG. 1, and during the screwing process both the acoustic emission that arises and the one measured by the force transducers 16 , 17 Clamping force in relation to each other is recorded. The recorded measured values can then be processed further using the method according to the invention in order to determine reference values for the characteristic curve or a table of values (see the description below) from the correlation between the acoustic emission detected and the measured clamping force of the screw connection.

In the following, an application example will be described with reference to FIGS . 3 to 5, using the method according to the present invention, from the acoustic emission arising during the screwing process, to determine the information required for exact determination of the clamping force in a form suitable for controlling a screwing device can.

First, in a calibration process, for example using the above described measuring device for several groups of screw against both the electrical derived from the acoustic emissions or optical signals as well as the clamping force detected to reference values to generate for later comparison. During disturbances (such as the Friction) vary significantly between the measuring groups, they become internal half of the individual measurement groups kept as constant as possible. Doing so for each screw connection, a table of values is created in which the electrical or optical signal and the synchronously measured values of the clamping force be filed.

In Fig. 3, two diagrams are shown, of which the upper diagram shows the time course of the clamping force of the screw connection measured via the force sensors in one step of a calibration process and the lower diagram shows the time course of the electrical or optical signal of the acoustic emission generated during the screwing process. This clearly shows that the maximum of the acoustic emission occurs at the point in time when the yield point of the screw and thus the maximum clamping force of the screw connection is reached.

A separate table of values is set up for each individual screw connection, ie for each step of the calibration process, in which the values of the clamping force and the associated values of the electrical or optical signal or - as described below - are further processed electrical or optical signal. In this way, the value table or characteristic curve between the clamping force and the signal is determined for each frequency band. In Fig. 4, a diagram is shown which shows the time course of the root mean square (RMS) of the electrical or optical signal's for several frequency ranges between 100 kHz and 450 kHz in steps of 50 kHz. In addition, the course of the measured clamping force over time is entered in FIG .

The electrical or optical signals of the individual measurement series are in the course of further processing by means of a Fourier transformation subjected to a frequency analysis and thus from the time domain to the Frequency range transformed, the width of the Fre Define frequency bands depending on the sensors used is. Alternatively, the electrical or optical signal can also be used Bandpass filters can be broken down into different frequency ranges. Dar the RMS value is then within the individual frequency bands or RMS signal, i. H. the root mean square of the signal.

To improve correlation of the measured electrical or opti to reach the signal with the clamping force, the RMS signal in be tegrated.  

In Fig. 5, two diagrams are shown, wherein the upper diagram the timing of the clamping force of the screw and the introduced into the screw torque and the lower slide program the timing of the RMS signal and the RMS integral to define the starting point for an offset Calculation and the integral calculation shows. As can be seen in Fig. 5, the starting point of the integration of the RMS signal can be determined so that the disturbing noises caused by the mounting and engaging of the screwing tool at the beginning of the screwing process and the noises that occur until the reaching of the so-called. Join point occur, have already subsided.

In this case, the integration of the RMS signal is started exactly when if the tightening torque, which is also measured continuously, in reaches a previously defined area. It is for the definition of the Starting point is irrelevant that due to fluctuating friction fluctuations in the amount of torque relative to the achieved Clamping force occur. It only has to be ensured that the joint point, d. H. the time after putting on and engaging the Is reached.

Alternatively, the integration of the signal supplied by the bandpass filter can be done first start after a predetermined offset, the offset from the integral is then subtracted.

The integral values of the electrical or optical signal are shown in Ver binding with the associated clamping force values for each frequency band and saved every screw connection. For later comparisons between the To be able to make different value tables, the clamping force  preferably divided into suitable stages in advance. The Abstu exercises are chosen so that the maximum error is about a toe nerpotenz is smaller than the maximum permissible for the screw connection Error.

A number of value tables is created for each group of measurements provides, which are then compared. To do this for all values of the RMS integral that are assigned to a specific clamping force net, the mean and the variance are formed. The variance can be estimated using known mathematical methods. Should the estimated variance is higher than a predetermined allowable Value, is with the examination of another frequency band or egg ner setting of the disturbance variables continued and the last Si Repeated signal processing step.

The value tables are then examined at what frequency tied the best correlation between the clamping force and the electrical or optical signal is present. It should be borne in mind that this Frequency band varies depending on the type and nature of the screw can be located. The frequency band is usually between 100 kHz and 400 kHz. From the values of the RMS integrals and the Clamping force is selected the table of values that on average the ge shows the least variance. This table of values or characteristic curve is used for the Control of screwdriving processes for the production of defined screwdrivers bonds in practice.

An optimal determination of the reference values can be achieved if the parameters of the screwing process, e.g. B. the later in the series ver  values that occur in practice for the tightening speed speed are known and taken into account in the calibration process. About it in addition, those interference parameters are preferably used in the calibration process varies, which act on the screw connection in practice, provided that this are known. In any case it is important that the disturbance of the friction is varied, the quantitative change being a subordinate Be has meaning, d. H. it does not necessarily have to be determined in practice become.

Another section of the method relates to the use of the screwing device in the manufacture of screw connections in practice:
In practice, a screwing process for producing a defined screw connection is carried out essentially like the calibration process described above. The screw connection can be made, for example, by means of a screwing device shown in FIG. 1. As described above, the sound pickup is preferably a piezoelectric sensor which is in contact with the screwdriver bit in the screwing tool and is therefore acoustically connected to the screw head during the screwing process. With the aid of the piezoelectric or optical sensor, the acoustic emissions occurring during the screwing process are recorded.

The acoustic emission measured for each screw connection becomes calculates the RMS integral in the previously determined frequency band and the Control of the screwing device supplied. Based on the comparison of the current signal (actual value) with that determined from the reference data  The reference value (target value) for the desired clamping force is time point determined at the end of the screwing process.

The following explains again in detail how the calibration process according to the invention and the subsequent practical use can proceed:
In order to be able to record the entire frequency spectrum of the signal during the calibration process, a multi-channel transient recorder is used for recording, for example, with which up to 10 ⁷ measurements per second can be carried out and saved. A computer with suitable analysis software can be used for data analysis.

With such a measuring system, the electrical or optical signal of acoustic emissions in the time domain are recorded, however from the noise that occurs during the screwing process device. In a first step, the signal is processed using a Fast Fourier Analysis or appropriate bandpass filters in the different fre frequency ranges, over which the effective value or the RMS Signal and the RMS integral is formed.

In the next step, a frequency band is determined, in which the a particularly good correlation between the Clamping force and the level of the integral signal result. To do this for each frequency band the tables of values under the same conditions performed screw connections analyzed. This creates a new who table that contains the variances of the clamping force. Under the advance  setting that the relative error of the clamping force in relation to the ordered absolute value of the clamping force over the entire force curve was kept constant, the variance of the integral values is almost the same.

Based on the maximum variance at hand, it can be estimated whether the examined frequency band and the assigned settings of the Disturbances are suitable, the required correlation with the required Ge to deliver accuracy. The based on the electrical or optical Si gnals determined in the corresponding frequency band compared with the clamping forces measured in the calibration process. should that Comparison result does not achieve the desired correlation, a another frequency band or a different group of measurements for bil reference data. Could reference values with the ge If the desired accuracy is determined, it becomes the control unit of the screwing device.

With an input on the control of the screwing device can In practice, the clamping force can be selected when tightening the screw connection should be reached. The control takes from the the associated level of the reference data stored as a value table preprocessed electrical or optical signal and stores it as the target value. After starting the screwing process, this is done via the Filtered and detected electrical or optical signal integrated after reaching the start value. The current integral value is fed to the control as an actual value. In the control, the ver carried out immediately between the target value and the current actual value. As soon as the target value is reached or exceeded, the screwdriver end by switching off the screw spindle.  

List of reference numbers

1

Screwdriver

2nd

Rotary drive shaft

3rd

Screwdriver bit

4th

Recording the screwdriver bit

5

Cap nut

6

Cavity in the rotary drive shaft

7

sensor

8th

Screw head

9

screw

10th

a component

10th

b component

11

lower component

12th

upper component

13

screw

14

Screw head

15

Counterpart

16

Load cell

17th

Load cell

18th

Guide pin

19th

Guide pin

20th

Base plate

Claims (14)

1. A method of operating a screw device for producing a defined screw connection ( 13 , 15 ), by means of which at least two components ( 11 , 12 ) are pressed against one another with a predetermined clamping force, characterized by the following method steps:

• - Detecting the acoustic emission that arises during at least one reference screwing process in a screw and / or the components to be clamped ( 11 , 12 ) and generating a corresponding electrical or optical signal,
• Extraction of at least two features from the electrical or optical signal using mathematical methods,
• Determining the feature whose course best correlates with the clamping force of the screw connection,
• Setting up the characteristic curve between the clamping force and the determined characteristic,
• - Configuration of a signal or Datenververarbeitungeinrich device such that the feature determined can be calculated directly from the elec trical or optical signal, and
• - Control and / or monitoring and / or process evaluation of the screwing operation depending on the determined characteristic and the signal supplied by the signal or data processing device.

2. The method according to claim 1, characterized in that

• - That a frequency analysis of the generated electrical or optical signal is carried out as part of the feature extraction,
• that the frequency band is determined in which there is the best correlation between the clamping force and the electrical or optical signal,
• that the characteristic curve between the clamping force and that signal component which lies in the determined frequency band is set to
• - That a the signal or data processing device bil dendes bandpass filter is set according to the fre qu frequency band determined, and
• - That the control and / or monitoring and / or process evaluation of the screwing process takes place depending on the characteristic he averaged and the signal supplied by the bandpass filter.

3. The method according to any one of the preceding claims, characterized, that in an evaluation unit that is currently from the signal or Da ver processing signal supplied with the characteristic ver is compared and based on the comparison result the current Is controlled, evaluated and / or documented.   4. The method according to any one of the preceding claims, characterized in that the clamping force of the screw connection ( 13 , 15 ) for determining the characteristic during the calibration method according to claim 1 via a force sensor ( 16 , 17 ) is determined, which between the two components ( 11 , 12 ) is arranged. 5. The method according to any one of claims 1 to 3, characterized in that the characteristic curve by simulating the behavior of the components ( 11 , 12 ) and / or the screw ( 9 ), by simulating the screwing process, by finite element methods and / or is determined by boundary element methods. 6. The method according to any one of the preceding claims, characterized, that the detection of the acoustic emission with a Tastfre frequency between 700 kHz and 1.3 MHz, preferably with an Ab sampling frequency of 1 MHz. 7. The method according to any one of claims 2 to 6, characterized, that the frequency analysis of the electrical or optical signal is carried out by means of a Fast Fourier transformation. 8. The method according to any one of claims 2 to 7, characterized,  that the determined frequency band between 100 kHz and 450 kHz is, the width of a frequency band is preferably approximately Is 100 kHz. 9. The method according to any one of the preceding claims, characterized, that the electrical or optical signal during the calibration process rens according to claim 1 and / or during practical use zes the screwing device amplified by an amplifier and / or processed using a preprocessing filter, in particular the latter is smoothed, preferably forming an effective value or an RMS signal is generated. 10. The method according to any one of claims 2 to 9, characterized by the following additional method steps which ge during the calibration method according to claim 1 and / or during the practical use of the screwing device:

• Calculating the integral of the signal supplied by the bandpass filter, the integral calculation beginning after a predetermined offset dependent on the respective screw connection,
• - Subtract the predetermined offset from the calculated integral.

11. The method according to claim 10, characterized by the following additional method steps, which are used during the calibration method according to claim 1 and / or during practical use of the screwing device:

• - Determining an additional measured variable that is characteristic of the respective screwdriving application,
• - Calculation of a characteristic corresponding to this measured variable,
• - Start the integral calculation depending on the measured variable he determined or in dependence on its course over time.

12. The method according to any one of the preceding claims, characterized in that the determined feature, in which the best correlation between the clamping force and the electrical or optical signal is present, transmitted to the screwing device, in particular to the screwing tool ( 1 ) of the screwing device and is used there for setting the signal or data processing device. 13. The method according to any one of the preceding claims, characterized in that the determined characteristic to the screwing device, in particular re to an outside of the screwing tool ( 1 ) arranged control unit of the screwing device is transmitted and stored there. 14. A method of operating a screw device for producing a deinstalled screw connection, by means of which at least two components ( 10 a, 10 b) are pressed against one another with a predetermined clamping force, characterized by the following method steps, which are used during practical use of the screw device:

• - Detecting the acoustic emission that arises during a screwing operation in a screw and / or the components to be clamped ( 10 a, 10 b) and generating a corresponding electrical or optical signal,
• - Determine the maximum of the electrical or optical Si gnals, which corresponds to the yield strength of the screw during screwing, and
• - End the screwing process shortly after reaching the maximum.