WO2001047669A1

WO2001047669A1 - Method, device and system for determining torque

Info

Publication number: WO2001047669A1
Application number: PCT/SE2000/002615
Authority: WO
Inventors: Christer Wallin; Jarl R Sobel; Ulf Carlqvist; Hans Ling; Jan Nilsson; Gheorghe Dutchevici
Original assignee: Abb Ab
Priority date: 1999-12-23
Filing date: 2000-12-21
Publication date: 2001-07-05
Also published as: AU2566601A; SE517560C2; SE9904784L; SE9904784D0

Abstract

A method and a device and system in which a torque applied to a bolt, screw or other fastener in a screw threaded joint using a pulse driven torque wrench is estimated. The pulse driven torque wrench is arranged with means for sensing torque applied by the pulse driven torque wrench, also with signal processing means and with control means to control the drive means. The present invention comprises memory and calculation means so that parameters may be calculated from measurements of torque applied. The applied torque is estimated from calculated parameters that describe the form of each pulse, enabling the applied torque to be accurately estimated. The main advantage of the invention is that it provides an accurate and consistent estimate of applied torque. It is also particularly fast and economic to use because no reset or re-calibration is needed for higher or lower torque values and for different fastener/joint combinations. The mode or rate of shut-off also may be pre-determined to suit the type of joint.

Description

Method, device and system for determining torque

TECHNICAL FIELD

The present invention relates to measurement of torque for industrial purposes. In particular, the present invention is a method, device and system, and computer program element for estimating the amount of torque applied by a pulse driven tool to a fastener in a screw threaded joint.

BACKGROUND ART It is a common requirement in many industries to fasten a bolt or other fastener in a screw threaded joint to a required torque setting during the assembly of components . A common and practical method for setting the torque of a fastener in a screw threaded joint is by using tools that work with torque pulses. The use of torque pulses makes the reaction force small, which means a machine such as a hand held torque wrench requires less physical effort to use it.

Pulse tools are often based on a fluid motor such as an air motor, powered for example by compressed air, with a torque converting means arranged between the fluid motor and the main shaft of the tool. Rotation of the fluid motor is transformed into a series of pulses in the torque converter means . The main shaft of the pulse tool is then indirectly driven by the fluid motor by means of pulses.

US 5,082,066 shows that a torque wrench may be shut off when a required torque setting has been reached with the aid of an inertial mass and a spring, which arrangement is adjusted up to the required torque level for a respective screw threaded joint. This required torque level must be reset on the torque wrench every time that the required torque changes or the type of fastener or joint changes. When the required torque level has been reached in the torque wrench the torque wrench stops applying force .

It is known from US 5,315,501 to use a compensating method with a rotary torque wrench. The method discloses that a torque wrench may be shut off early so that torque overshoot in a rotary tool does not cause a required torque value to be exceeded. Torque value in this example of a continuously acting wrench is measured by a transducer directly coupled between a drive shaft of the rotary torque wrench and the head of the fastener. De-acceleration times of a number of tightening sequences are measured, and a constant of a linear function is estimated for a series of tightenings of a particular screw threaded joint. Thereafter, a correction is applied to compensate for a tendency of the torque wrench to overshoot the torque value that was specified. However this method only deals with torque settings in excess of a target value due to overshooting by the tool, and does so only on the basis of torque settings that are measured by a transducer directly coupled to a tool drive shaft.

Another approach to shutting off a torque wrench when the required torque setting has been reached is to include a torque sensing device in the torque wrench. The torque applied by the torque wrench to the fastener is measured and the tool is shut off when the measured torque reaches the required torque. EP 502 748 for example discloses a pulse driven torque wrench that includes a magneto-electric transducer means arranged with the main shaft of the torque wrench so as to measure torque in the main shaft that is applied to a fastener by the torque wrench. However, a problem with this approach is that the torque in the shaft of a tool tightening a fastener in a screw threaded joint may not always be the same as the torque applied between the mating surfaces of the screw threads of the joint.

The reasons for this are complex and difficult to isolate. It is due in part to dynamic changes depending on elasticity and inertia of the fastener and elasticity of the joint. The important point is that a difference between the torque measured in the shaft of a tightening tool and the torque achieved in a screw threaded joint may result in an error in the actual torque in the tightened screw threaded joint, especially with a non-continuously acting wrench such as a pulse driven torque wrench.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method to estimate the torque applied to a bolt or other fastener in a screw threaded joint.

It is another object of the invention to provide an accurate method of estimating the torque applied which method is independent of joint type and independent of required torque value.

It is a further object of the invention to provide a device and system for carrying out the method to estimate the torque applied to a bolt or other fastener in a screw threaded joint.

It is a yet further object of the invention to provide a computer program element to carry out the method. The present invention defined by the appended claims and comprises a method according to claim 1 and a device and system according to claim 17, and the use thereof according to claim 31 and a computer program element according to claim 32. The present invention may be summarily described as a method to determine an estimated torque applied to a bolt or other fastener in a screw threaded joint using a pulse driven torque wrench. The pulse driven torque wrench is arranged with means for sensing torque applied by the pulse driven torque wrench to the fastener, and may also comprise control means to control the drive means . The present invention is carried out by using memory and calculation means so that parameters may be calculated from measurements taken of torque applied during each pulse. The parameters that are calculated describe characteristics of each pulse in a series of torque pulses.

Based on the acquired set of parameters a value of tightening torque is estimated, according to a relationship described below.

The principal advantage of the invention is that it provides an accurate and consistent estimate of applied torque. The invention is also particularly fast and economic to use because no reset or re-calibration is needed for higher or lower torque values of different fastener/joint combinations. The same pulse driven tool may thus be used for different torque settings in the same assembly job without adjustment or calibration. As well as technical improvement due to accuracy, the invention is further economically advantageous and useful as it may be applied to a wide range of jobs. No special training is needed to operate it and accuracy of this pulse driven wrench is virtually operator independent. A further advantage is that the operation of the tool may be tailored according to the job and the joint type. This may be done, for example once a predetermined torque value has been reached, by selecting a control action from among various types of fast or slow changes to pulse form, and shut-offs, provided by a pulse driven torque wrench according to an embodiment of the present invention. Furthermore, fastening data generated by the pulse driven torque wrench may be logged and stored for calibration, certification and record keeping purposes.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described in more detail in connection with the enclosed drawings .

Figure 1 shows schematically a pulse driven torque wrench according to the present invention. Figure 2 shows torque versus time diagrams for a series of pulses applied to a hexagonal headed bolt in a hard joint.

Figure 3 shows torque versus time diagrams for a series of pulses applied to a socket headed bolt in a hard joint.

Figure 4 shows in a diagram of torque versus time parameters of a pulse form that may be calculated according to the present invention.

Figure 5 shows a diagram of results using an estimated torque calculated as peak torque in the last pulse only, for different joints, according to the PRIOR ART. Figure 6 shows a diagram of results using an estimated torque calculated using peak torque in the last pulse as a parameter, according to an embodiment of the invention.

Figure 7 shows a diagram of results of estimated torque calculated using peak torque, maximum rate of torque increase, and torque increment as pulse parameters according to a preferred embodiment of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a pulse driven torque wrench 1 in which a drive shaft coupled to drive means 2 is arranged as a first drive shaft part 5 and a second drive shaft part 4. A torque sensing means 3 is coupled between the first drive shaft part 5 and the second drive shaft part 4 of the torque wrench 1. The second drive shaft part 4 is arranged to grip a bolt, screw or other threaded fastener 7. The fastener 7 is shown in position in a screw threaded joint 6. The torque sensing means 3 is connected to a signal processor 8 equipped with a calculation means 9 and a memory means 10. The signal processor 8 and the pulse driven torque wrench 1 are further connected to a controller 11. Signal processor 8 sends a signal 15 containing the estimated torque to controller 11. Controller 11 is arranged capable of generating a control signal, indicated in Figure 1 by the number 16, to control drive means 2.

In a method according to the PRIOR ART a value of tightening torque is determined as peak torque value in the last pulse, which results in a substantially linear function between discrepancy and detected torque with a relation that varies considerably between different joint types. This may be seen in Figure 5 (according to the Prior Art) which shows a mean deviation between determined and actual torque values for different torque levels and different joints, where the torque has been determined as peak torque alone in the last pulse. Figure 5 shows the mean deviation found for increasing torque values for four different fastener/ j oint combinations: socket headed/hard 51, socket headed/soft 52, hexagonal head/hard 53, and hexagonal head/ soft 54. In other words, a measurement of peak torque alone during the last pulse does not give an accurate measure or estimate of torque applied in the joint. According to the present invention the torque may be continuously measured by torque sensing means 3 or may be sampled resulting in several samples during each torque pulse. A series of parameters 12, 13, 14 are calculated from the torque measured over time by torque sensing means 3 during the tightening of a fastener 7 in the screw threaded joint 6. The pulse driven torque wrench 1 includes a torque sensing means 3 such as a agnetoelastic torque transducer. Preferably a magnetoelastic transducer of the Torductor-S type manufactured by ABB is used. Parameters 12, 13, 14 calculated from torque measurements in calculation means 9 are stored in the memory means 10 of signal processor 8. Further calculations are performed by the calculation means 9 to produce an estimated torque M of the actual tightening torque in the screw threaded joint 6. The signal processor 8 is connected to the controller 11. A value of estimated torque M is calculated in calculation means 9 , which value is sent to controller 11 as signal 15, and is compared to a predetermined required torque value R.

When the estimated torque M is found to be within a predetermined value of the required torque R the controller 11 generates a control signal 16 which is sent to the drive means 2 of the pulse driven torque wrench 1. The control signal 16 influences the action of the drive means 2 once estimated torque is within a predetermined value of required torque R.

In a development of the invention the drive means 2 is shut off when estimated torque M is within a predetermined value of required torque R so that no more pulses are generated. In another development of the invention the operation of drive means 2 is changed by control signal 16 such that when estimated torque M is within a pre-determined value of required torque R, a series of pulses with a substantially limited increment in torque between pulses is produced, resulting in a more gradual approach to the required torque R. In this way, both the mode of shut-off and the rate of shut- off may be predetermined. Even other control schemes are conceivable that are based on the difference between estimated torque M and predetermined value of required torque R. In another development of the invention the estimated torque is used to monitor the tightening operation, without being used directly in the control action.

Figure 2 shows a series of torque pulses in which a hexagonal headed bolt in a hard joint is tightened to an estimated torque of, in this example, 63 Nm.

Figure 4 shows an example of one such torque pulse that may be calculated according to the present invention, with some of its associated parameters. It shows an example of a pulse form 40 including a peak torque 41, a maximum rate of increase of torque 42 and a centre of symmetry 43 in the time (x) direction of the pulse form 40. The term pulse form as referred to in the text means the shape of a curve formed by values of torque during a time period of a pulse as well as an area enclosed by the curve, as well as values of torque under the duration of a pulse. The pulse form and the characteristics that it comprises may be represented by parameters calculated in many different ways, as will be further described below.

During the tightening operation the torque detected by the torque sensing means 3 in the pulse driven torque wrench 1 during each pulse is continually recorded. The measurements of torque made by the torque sensing means 3 as a function of time are used to calculate parameters that describe the pulse for , including :

Maximum torque for the complete time interval

Mean torque of the pulse

Centre of gravity of pulse form 43 in time (x) or torque (y) direction Sum of torque increments between samples within a pulse

Peak position of torque within a pulse in time (x) direction Maximum rate of increase of torque 42 during a pulse Rise time, this being time between 10% to 90% of pulse growth Pulse width (time from 50% of the rise flank till 50% of the fall flank)

Torque impulse, which is the integral of torque with respect to time as a measure of energy in the pulse Time increment, which is time between the pulses The number of pulses Pulse number, the position of any pulse in a series of consecutive pulses

According to the invention, torque during a pulse and one or more of the parameters, such as those which may be obtained as statistical measures, measurement values, integers, differential values, and integral values previously listed, are calculated and stored in signal processor 8.

Figure 3 shows a series of torque pulses similar to those shown in Figure 2 applied to a socket headed bolt in a hard joint . Figures 2 and 3 show tnat the pulse form varies significantly between the first and last pulse. This shows that it is not only the peak torque in a pulse that changes, increasing through the series, but also that the rate of increase of torque as well as other parameters vary during the course of the series . The changing form of each pulse as illustrated in Figures 2 and 3 is substantially consistent for every repetition of a tightening operation on the same fastener/joint combination.

In addition, Figure 2 and 3 also show that the pulse form for different types of fastener may be markedly different. It is clear from comparing the pulse forms of these two types of bolt that the pulse form in a series of pulses applied to the hexagon headed bolt shown in Figure 2 may be very different from the pulse form recorded for the socket headed bolt as shown in Figure 3.

According to the present invention an estimated tightening torque based on said pulse parameters from a pulse sequence may be calculated according to the following general expression :

where

M is said estimated torque

P_ι,P_j are pulse parameters k₀ is a constant offset k_l, k_{ι ι} are torque wrench specific constants Suitable pulse parameters from the pulse sequence may be chosen based on their influence on the result and their readiness to be calculated. The constants k_t for a specific type of pulse driven torque wrench may be determined according to a method described later in the description. Even higher order terms or other mathematical functions may be included in the expression to give a closer correlation to an actual tightening torque.

In the preferred embodiment of the invention, three parameters are calculated and used to calculate estimated torque M . These parameters correspond to the numbers 12, 13, and 14 indicated in Figure 1 which are calculated in signal processor 8 from measurements made by torque sensing means 3. Parameters 12, 13, and 14 are calculated during a first pulse and a second pulse. From these parameters 12, 13, and 14 a value may be calculated for estimated torque M in the screw threaded joint .

The parameters describe the form of the first and the second pulse, and are preferably: -Maximum torque during the second pulse,

-Maximum rate of increase of torque during second pulse, -Peak torque during the first and second pulse.

A calculation employed in the calculating means 9 in the preferred embodiment uses the following equation:

M = k₀ +k_ip_M/ +k₂p_JMj + fc,⁽ .,_tI - P_u ⁾ + _{IM l} ^(p^ , - ^pM, ⁾ where

M is the estimated torque P_M is a pulse parameter corresponding to the maximum torque of the second pulse P_M is a pulse parameter corresponding to the maximum torque of the first pulse P_m is a pulse parameter corresponding to the maximum rate of increase of torque of the second pulse k₀,k ,k₂ ,k_?ι, k₄ are constants specific for each type of pulse driven torque wrench

Accurate and consistent results for an estimated torque M calculated using maximum rate of increase of torque, torque increment, peak torque value compared to the actual torque are shown in Figure 7 for hexagon and socket headed bolts in hard and soft joints. The mean value of the discrepancy between estimated and actual torque is significantly reduced, with almost negligible difference between different joints and torque levels . It may be seen by comparing the results shown in Prior Art Figure 5 with the results shown in Figure 7, that the method according to the invention of estimating the torque from the parameters as described is more accurate than the PRIOR ART method of measuring only the torque in the last pulse only. Figure 7 shows four fastener/joint combinations indicated as socket headed/hard 71, socket headed/soft 72, hexagonal head/hard 73, and hexagonal head/soft 74.

The invention is carried out according to the preferred embodiment using a pulse driven torque wrench 1 connected to signal processor 8 and controller 11 as indicated in the schematic diagram of Figure 1. In the preparation for first use of a particular type or model of pulse driven torque wrench 1 for a fastening operation, a test is made in which a number of fasteners are tightened in a number of selected screw threaded joints. The purpose of the test is to provide data to establish values for the mechanical constants described below. The constants may have to be determined for each type of pulse tool, but not necessarily for every different fastener/joint combination. In particular, it is not necessary to determine values for the constants for every different torque setting for similar fastener/ joint combinations. The constants k_t are found from statistical analysis of torque measurements per type of torque wrench compared to actual torque.

To collect data for such a test, measurements are taken of torque as a function of time for each pulse in a series during each tightening operation. Calculation of estimated torque M is done using an equation as previously described, for example. Measurements are also made of actual torque achieved during test fastenings, and then compared with estimated torque. A standard statistical analysis is performed to determine, for the specific torque wrench type, a value for constants k_: used in an equation of the type previously described.

The actual torque achieved during each tightening operation may be compared to the estimated torque calculated during a tightening operation such as those shown in Figures 2 and 3. After the bolts or other fasteners have been tightened, each joint is investigated to measure the actual torque that was achieved during tightening, for example with a method as described in US 4,450,727. The estimated torque is then compared to actual torque for a number of varying torque values for each different type of fastener in different types of screw threaded joint. The actual torque may also or alternatively be determined by measuring the torque directly in the joint or in the fastener during the tightening operation.

In the case in which a mathematical model or description exists for the particular type or model of the pulse driven torque wrench 1, a mathematical analysis or mathematical simulation may be used to calibrate the method according to the invention, for the purpose of determining values for the constants k_t or coefficients .

According to another, simpler embodiment of the invention Figure 6 shows a diagram of the mean deviation between estimated and actual torque values after the application of an estimated torque M calculated using peak torque in the last pulse only as a parameter according to the invention. It shows that the mean deviation between estimated and actual torque values differs for each type of joint. In Figure 6, the different fastener/joint combinations are shown as: socket headed/hard 61, socket headed/soft 62, hexagonal head/hard 63, and hexagonal head/soft 64.

The above simple embodiment of the invention shows a clear improvement of the results compared to PRIOR ART in Figure 5. However, it does not reach the same accuracy as the preferred embodiment as shown by the diagram of Figure 7. The inclusion in the preferred embodiment of more than one parameter as well as the inclusion of at least one interaction term provide significantly improved accuracy. In another embodiment of the invention, the pulse form of the first and the second pulse may be described using parameters calculated using another method of signal processing. The following may be used to describe the form of one or more pulses :

Fourier transform, Fourier series, cosine and sine transform, cosine and sine series, and wavelets. Any transformation or decomposition may be applied in a time domain or a frequency domain to torque pulses to obtain one or more sets of fundamental functions or base functions as alternate methods to calculate pulse parameters describing a first and a second torque pulse.

In another embodiment of the invention an estimated value of a clamping force F is calculated from the parameters previously listed and described. The clamping force is the resulting compressive force in the joint exerted by the tensile force in the fastener. The method is calibrated using the same methodology as when it is used for determining estimated tightening torque. It is based on a measurement of actual clamping force in a joint together with the collection of pulse parameters of a series of different fastener/ joint combinations. Different calibration may need to be performed for different types of pulse tool and may also be needed for different fastener/joint combinations. The actual clamping force may be measured in the joint or in the fastener during the fastening operation or after the fastening operation and the measurements used to determine a series of constants or coefficients used in the expression for estimated clamping force F . A method for measuring the clamping force directly in the fastener is described in US 4,846,001. In a further embodiment of the invention parameters of the pulse may be measured with respect to the angular rotation of the fastener 7 instead of with respect to time. Measurements of torque made by the torque sensing means 3 as a function of the angular rotation of the fastener 7 are used to calculate at least one of the parameters previously described that describe the pulse form. In practice this is achieved by including an additional means to measure angular rotation and angular position accurately during fastening, a device such as an angular sensor, an optical sensor, or inductive means such as a resolver. Torque may also be estimated from a combination of parameters calculated from both measurements of torque with respect to angular rotation as well as with respect to time.

In the best use of the invention, the measurements collected by torque sensing means 3 and parameters calculated in the signal processor 8 are supplied to a local or remote data storage and analysis unit, such as a data logger or network computer. This data may be used, for example, for quality records, calibration purposes, certification or record keeping purposes .

The name pulse driven torque wrench used in this description to refer to the present invention is not an exclusive description, and the general principles disclosed apply to any pulse driven wrench, impact wrench, nut runner, screw driver or similar device that may be used to tighten a screw threaded fastener to a required torque. The drive means 2 may be any suitable drive means, such as a pulse generating means which is powered by air or hydraulic fluid, or another source including an electric motor suitably arranged for delivering torque as one or more non-continuous pulses . The invention described is not limited to the embodiments that have been described but may instead according to general principles disclosed result in a number of different practical embodiments. Figure 1 shows schematically a pulse driven torque wrench 1 connected to means such as the signal processor 8 and controller 11. However a pulse driven torque wrench 1 may equally include one or more of the signal processor 8 or calculating means 9 or controller 11 within the main housing, structural parts or body of the tool as electronic circuits on boards or in chips according to the known techniques for making miniature control circuits . Furthermore, any function of the present invention such as for example the signal processor 8 or controller 11 may equally be implemented as software functions by computer program code, or by one or more computer program elements, within a computer program in a computer, microprocessor or micro-chip connected to or incorporated for that purpose in a pulse driven torque wrench 1.

The invention is not limited to the embodiments described, but to a number of modifications within the reach of the person skilled in the art that are feasible within the scope of the claims. For example other parameters of the torque measurements, such as those listed in this description as well as others that may be calculated from measurements of torque over time but are not explicitly described, may comprise any kind of calculable quantitative measure of torque and/or of torque versus time, including standard transform and decomposition methods and statistical methods including Multivariate Analysis (MVA) Principal Component Analysis (PCA) and Projection to Latent Structures (PLS), and other combinations of parameters, which may be used in calculations related to determininc an estimated value for the torque in a screw threaded joint are within the scope of the claims.

Claims

1. A method to determine an estimated torque M applied to a fastener (7) in a screw threaded joint (6) using a pulse driven torque wrench (1) arranged with means (3) for sensing torque applied by the pulse driven torque wrench (1) to the fastener (7), in which a torque in a pulse is measured, characterised in that the method comprises the steps of -measuring with said torque measuring means (3) the torque applied to the fastener (7) during a first pulse and a second pulse.

-calculating one or more pulse parameters that describe the form and/or characteristics of the first pulse and the second pulse

-calculating said estimated torque M dependent on the one or more pulse parameters .

2. A method according to claim 1, characterised in that the one or more pulse parameters comprise a statistical measure, an integer, a differential expression, or an integral expression of a quantitative measure of a characteristic of torque and/or of torque with respect to time.

3. A method according to claim 2, characterised in that the pulse parameters comprise one or more of: Maximum torque of the pulse

Mean torque of the pulse

Centre of gravity of the pulse in time (x) or torque (y) direction

Sum of torque increments between samples within a pulse Peak position of torque within a pulse in time (x) direction

Maximum rate of increase of torque during a pulse

Rise time

Pulse width Torque impulse

Time increment, which is time between the pulses The number of pulses

Pulse number, the position of the pulse in a series of pulses

4. A method according to claim 3, characterised in that the estimated torque is calculated with an expression of the form: n n m

M= *₀ + ∑k,P, + ∑ ∑k,^p,^p,

;=1 ι=l /=! where M is said estimated torque

P_t,P are pulse parameters k₀ is a constant offset k k are torque wrench specific constants

5. A method according to claim 4, characterised by the step of -calculating said estimated torque according to:

M = k, + k P_Mj + k₂P_{M ι} + k, P_{M ti} - P_M ) + k₄P_IM (P_{M ιi} - P_M ) where

M is said estimated torque P_M is a pulse parameter corresponding to the maximum torque of the second pulse P_M is a pulse parameter corresponding to the maximum torque of the first pulse P_dM is a pulse parameter corresponding to the maximum rate of increase of torque of the second pulse k₀,k_x ,k₂,k^, k are constants specific for a type of pulse driven torque wrench

6. A method according to claim 5 , characterised in that the pulse driven torque wrench (1) comprises control means to control the drive means (2) and the method comprises the further steps of

-comparing said estimated value of M with a required torque value R -generating a control signal (16) depending on a difference between said estimated torque M and the required torque R, -influencing by means of the control signal (16) the action of the drive means (2) .

7. A method according to claim 6, characterised in that the control signal (16) is arranged to control drive means (2) such that a following pulse has different characteristics than said second pulse such that the pulse form is changed.

8. A method according to claim 7, characterised in that the control signal (16) is arranged to control drive means (2) such that a following pulse has an increment of estimated torque which is reduced compared to the second pulse.

9. A method according to claims 6-8, characterised in that the control signal (16) is arranged relative to drive means (2) to influence the drive means (2) such that no more than a predetermined and limited number of pulses are produced.

10. A method according to any of the claims 6-9, characterised in that the control signal (16) is arranged relative to drive means (2) to influence the drive means (2) such that the drive means is shut off.

11. A method according to claim 2, characterised in that the one or more pulse parameters comprise a quantitative measure of a characteristic of torque measured with respect to angular rotation .

12. A method according to claim 1, characterised in that one or more of the pulse parameters comprise calculation by means of any of a Fourier transform, a Fourier series, or a wavelet transform.

13. A method according to claim 1, characterised in that an estimated clamping force is calculated from the pulse parameters .

14. A method according to claim 13, characterised in that the estimated clamping force is calculated using values for constants of the type k_: .

15. A method according to claim 1, characterised in that the steps of calculating pulse parameters and calculating estimated torque are integrated into one step.

16. A method according to claim 1, characterised in that the second pulse is the last pulse of a series of pulses.

17. A device and system for tightening a fastener (7) in a screw threaded joint (6) comprising a pulse driven torque wrench (1) with a drive means (2) and a torque sensing means (3) arranged to measure the torque applied to said fastener (7) , characterised in that said device and system comprises a signal processor (8), a memory means (10) and a calculating means (9) in which

-said torque sensing means (3) is connected to said signal processing means (8) -the signal processing means (8) contains the calculation means (9) for calculating parameters that describe the form of each pulse,

-the memory means (10) is arranged suitable for storing torque values and parameters that describe the form of each pulse,

-the calculation means is further arranged for calculating the estimated torque M applied to said fastener (7) .

18. A device and system according to claim 17, characterised in that the signal processing means (8), calculation means (9) and memory means (10) comprises means to calculate pulse parameters of the first or second pulse from torque values as a function of time, pulse parameters comprising one or more of: Maximum torque of the pulse

Mean torque of the pulse

Centre of gravity of the pulse in time (x) or torque (y) direction

Maximum rate of increase of torque during a pulse

Rise time

Pulse width

Torque impulse Time increment, which is time between the pulses

The number of pulses

Pulse number, the position of the pulse in a series of pulses

19. A device and system according to claim 18, characterised in that the signal processing means (8) contains an algorithm for calculating said estimated torque M with an expression of the form:

where

M is said estimated torque

P_ι,P_/ are pulse parameters k₀ is a constant offset k_l, k_{l /} are torque wrench specific constants

20. A device and system according claim 19, characterised in that the signal processing means (8) contains an algorithm for calculating said estimated torque M which is of the form

M = k_Q + k_xP_M) + k₁P_dUj + k, P_{M ιi} - P_M ) + k₄P_IM (P_{M f} - P_M ) where

M is said estimated torque

P_M is a pulse parameter corresponding to the maximum torque of the second pulse

P_M is a pulse parameter corresponding to the maximum torque of the first pulse P_dM is a pulse parameter corresponding to the maximum rate of increase of torque of the second pulse k_] ,k₂k_7tk₄ are constants measured for each type of pulse driven torque wrench.

21. A device and system according to claim 20, characterised in that -the signal processing means (8) is connected to a controller (11) -the controller (11) is arranged to compare said estimated value of torque M with a pre-determined required value for torque R -controller (11) is further arranged to generate a control signal (16) to control the drive means (2) of the pulse driven torque wrench (1) when M is within a predetermined value of R.

22. A device and system according to any of claims 17 or 18, characterised in that it comprises a means for measuring angular rotation such that torque is measured with respect to angular rotation.

23. A device and system according to claim 21, characterised in that the control signal (16) is arranged to control the drive means (2) such that the form of each pulse is changed.

24. A device and system according to claim 23, characterised in that the control signal (16) is arranged to control the drive means (2) such that the increase of torque in a pulse following the second pulse is reduced.

25. A device and system according to claim 23, characterised in that the control signal (16) is arranged to control the drive means (2) so as to stop drive means (2) following the second pulse.

26. A device and system according to claim 25, characterised in that the signal processor (8) with memory means (10), and calculation means (9) and the algorithm for calculating estimated torque M and comparing it with required torque R are arranged as integrated circuits and/or electronic devices.

27. A device and system according to claim 26, characterised in that one or more parts of the integrated circuits and/or electronic devices, iε incorporated inside the pulse driven torque wrenc .

28. A device and system according to claim 26, characterised in that one or more of parts of the signal processor (8), calculation means (9), memory means (10), or controller (11) are arranged as circuits integrated inside a computer or a computerised control unit and the one or more parts of signal processor (8), memory means (10), calculating means (9), controller (11) are implemented as a computer program product inside a computer, a microprocessor or a control unit.

29. A device and system according to claim 28, characterised in that one or more of the computer, the microprocessor or the control unit is incorporated inside the pulse driven torque wrench .

30. A device and system according to any of the claims 17-29, characterised in that the signal processor (8) , memory means

(10) calculating means (9) are arranged such that the steps of calculating pulse parameters and calculating estimated torque are carried out in one step.

31. Use of a device and system according to any of the claims 17-30 to determine the torque applied to a threaded fastener (7) .

32. A computer program element incorporating computer program code arranged to make a general purpose computer or microprocessor carry out one or more steps of a method according to any of the claims 1-17.

33. A computer program element according to claim 32 characterised in that it includes an algorithm according to the equation of claim 19.

34. A computer program element according to claim 32 characterised in that it includes an algorithm according to the equation of claim 20.

35. A computer program element according to claim 32 included in a computer readable medium.

36. A computer readable medium including computer program code according to claim 32.