TECHNICAL FIELD

The invention relates to a method and system for working of a workpiece using a work tool, according to the appended claims.

BACKGROUND AND PRIOR ART

A reliable and repeatable hole quality may be essential, for instance in structurally important, load bearing, aerospace applications. The hole quality may depend on type of working tool, such as a hole making apparatus, type and quality of the cutting tool, process parameters, tool wear and type of material in which the hole is produced.

Different types of hole making apparatuses are available. For special applications such as hole making in the aircraft structure of an aircraft the demands of accuracy are extremely high and therefore special hole making apparatuses should preferably be provided. Such a special hole making apparatus may use the twist drill technique where the cutting tool rotates around its own axis while axially being fed through the material. The twist drilling method may also be vibration assisted where the feeding motion fluctuates somewhat in the axial direction with a chosen frequency and amplitude. Such a special hole making apparatus may also use the orbital drilling technique. Orbital drilling is based on machining the material both axially and radially by rotating the cutting tool about its own axis as well as eccentrically about a principal axis while feeding the cutting tool through the material.

One type of hole making apparatuses uses a nosepiece for, which may comprise a clamping means and a cutting tool. The nosepiece is configured to be positioned in a template mounted at the work piece. The template may comprise guide openings in which the nosepiece of the hole making apparatus is to be positioned.

The nosepiece may be subjected to large axial forces when drilling is performed. The nosepiece being positioned in the template may be clamped to the template in the best manner possible for holding the nosepiece in position relative the plane of the template. The documents US6872036 B2, EP 0761351 B1 , US 20080145160 A1 and US 548241 1 A disclose different types of drilling machines, which may use a template. The template may comprise a sleeve positioned in opening of the template for guid- ing a nosepiece of the drilling apparatus.

SUMMARY OF THE INVENTION

There is a need to further develop a method and a system for a work tool which overcome problems of prior art. There is also a need to develop a method and a system for a work tool, which can be used for high axial forces acting upon the work tool.

There is also a need to develop a method and a system for a work tool, which is cost- effective.

The object of the invention may therefore be to further develop a method and a sys- tern for a work tool which overcome problems of prior art. Another object of the invention may be to develop a method and a system for a work tool, which can be used for high axial forces acting upon the work tool. Another object of the invention may be to develop a method and a system for a work tool, which is cost-effective. The herein mentioned objects may be achieved by the above-mentioned method and a system for a work tool according to the independent claims.

According to the invention the method of working of a workpiece using a work tool, said workpiece having attached thereto a template with preformed guide openings lo- cated in a pattern corresponding to the positions of holes to be formed in the work- piece, said work tool may be provided with a nosepiece configured for fixating the work tool relative the guide openings by exerting a clamp force between the nosepiece and an interior wall of the respective guide opening. The method may comprise the steps of:

-increasing the coefficient of friction on the surface of said interior wall of the guide opening and/or on the surface of the nosepiece;

-positioning the nosepiece in one guide opening; and

working of the workpiece. Such a method may overcome the problems of prior art and may be used for a work tool which applying high axial forces acting upon the work tool. Such a method may also be cost-effective. By the method the work tool can be held firmly in position relative the template even if high axial forces are due when forming the hole in the work- piece. Feeding a cutting tool attached to the work tool axially towards and through the workpiece may induce large axial forces on the work tool. These axial forces may move the work tool in relation to the template during the working process. However, when increasing the coefficient of friction on the surface of said interior wall of the guide opening in the template and/or on the surface of the nosepiece, the work tool may be firmly held in the template and may not move in relation to the template. This may improve the overall quality of the machined hole in the workpiece. When the fixation of the work tool to the template is increased a larger diameter of the cutting tool may be used. A larger diameter of the work tool may need increased axial forces acting on the work tool. Thus, instead of using different cutting tools, such as drills, in steps, having different diameters, a single cutting tool having a large diameter may be used for finishing the hole in the work piece. Using a single cutting tool for finishing the hole in the work piece may be cost-effective. Increasing the coefficient of friction on the surface of said interior wall of the guide opening and/or on the surface of the nosepiece may be accomplished by treatment of the surface of said interior wall of the guide opening and/or on the surface of the nosepiece. The treatment may comprise a mechanical treatment, such as grinding of the surface of said interior wall of the guide opening and/or on the surface of the nosepiece. The treatment may comprise a chemical treatment, such as applying a chemical substance on the surface of said interior wall of the guide opening and/or on the surface of the nosepiece.

According to an aspect of the invention the step of working of the workpiece may be preceded by a step of controlling the clamp force between the nosepiece and the template. The clamp force between the nosepiece and the template may be controlled so that the work tool can be held firmly in position relative the template when forming the hole in the workpiece.

According to a further aspect of the invention the coefficient of friction on the surface of the template and/or on the surface of the nosepiece may be increased by means of a surface coating. The surface coating may be applied on the surface of the template and/or on the surface of the nosepiece, so that the surfaces are covered by the coating. However, as an alternative only fields or spots on the surface of the template and/or on the surface of the nosepiece may be applied with the surface coating. The surface coating may have features that increases the coefficient of friction on the surface of the template and/or on the surface of the nosepiece, so that the work tool may be firmly held in the template and may not move in relation to the template during the working process. According to a further aspect of the invention the surface coating may comprise diamonds. The diamonds may have a size and a form of small particles incorporated in the surface coating. Such surface coating, comprising diamonds, may have features that increases the coefficient of friction on the surface of the template and/or on the surface of the nosepiece, so that the work tool may be firmly held in the template and may not move in relation to the template during the working process.

According to a further aspect of the invention the clamp force between the nosepiece and an interior wall of the respective guide opening may be controlled by means of an electrical machine. An electrical machine may be accurately controlled and thus also the clamp force between the nosepiece and an interior wall of the respective guide opening may be controlled accurately. The clamp force may be adapted to the axial forces that may act on the work tool during the working process. Increasing the clamp force may prevent the work tool to move in relation to the template during the working process.

The electrical machine may be an electrical linear drive motor which drives a drive rod. The drive rod may be directly connected to the nosepiece for exerting the clamp force between the nosepiece and an interior wall of the respective guide opening. Alternatively, the drive rod may be coupled to a linkage arrangement, which may in turn be coupled to the nosepiece. By operating the electrical machine the nosepiece may exert a clamp force between the nosepiece and an interior wall of the respective guide opening in a controlled manner and with a controlled force. A control unit may control the electrical machine to move the rod and thereby control the clamping force between the nosepiece and the template. According to a further aspect of the invention the positioning of the nosepiece in one guide opening may be provided by means of a robot apparatus. This may reduce the time for finishing the working process. In addition, the overall quality of the finished holes in the workpiece may be increased.

According to a further aspect of the invention, the step of increasing the coefficient of friction may be followed by a step of determining a desired value of the clamp force for fixating the work tool relative the guide opening. The clamp force may be adapted to the coefficient of friction on the surface of the template and/or on the surface of the nosepiece. Adapting the clamp force for fixating the work tool relative the guide opening may prevent the work tool to move in relation to the template during the working process.

According to a further aspect of the invention an actual value of the clamp force may be detected and compared with said desired value by a loop execution. By detecting the actual value of the clamp force and adapting the clamp force for fixating the work tool relative the guide opening ta a desired value of the clamp force by a loop execu- tion, the work tool may be prevented to move in relation to the template during the working process.

According to a further aspect of the invention the step of increasing the coefficient of friction on the surface of said interior wall of the guide opening guide opening may in- elude providing by a bushing in the template, which bushing has said interior wall. When a bushing is provided in the guide opening, the coefficient of friction on the surface of the bushing may be adapted for increasing the fixating of the work tool relative the guide opening and thus preventing the work tool to move in relation to the template during the working process.

According to a further aspect of the invention the work tool may be a drilling machine comprising a rotary cutting tool or is an orbital drilling apparatus. According to a further aspect of the invention, the step of working of the workpiece may comprise a hole-cutting process performed in the workpiece.

According to the invention the system for working of a workpiece uses a work tool. Said workpiece may have attached thereto a template with preformed guide openings located in a pattern corresponding to the positions of holes to be formed in the workpiece, said work tool may be provided with a nosepiece configured for fixating the work tool relative the guide openings by exerting a clamp force between the nosepiece and an interior wall of the respective guide opening. The system may comprise means for increasing the coefficient of friction on the surface of said interior wall of the guide opening and/or on the surface of the nosepiece; means for positioning the nosepiece in one guide opening and means for working of the workpiece.

Such a system may overcome the problems of prior art and may be used for a work tool which applying high axial forces acting upon the work tool. Such a system may also be cost-effective. By the system the work tool can be held firmly in position relative the template even if high axial forces are due when forming the hole in the work- piece. According to an aspect of the invention the means for increasing the coefficient of friction on the surface of the template and/or on the surface of the nosepiece may be a surface coating.

According to an aspect of the invention the system may comprise an electrical ma- chine for controlling the clamp force between the nosepiece and the template.

According to an aspect of the invention, a clamping sleeve may be slidingly arranged around a nosepiece which clamping sleeve may be configured to be moved along the central axis by means of an electrical machine coupled to a control unit. The nosepiece may comprise first and second conical clamping sleeves, which are axially displaceable in relation to each other. The first clamping sleeve may embrace the second clamping sleeve. The first clamping sleeve may be displaceable in relation to the second clamping sleeve by means of the electrical machine. The electrical machine may be coupled to a control unit for controlling the expansion of the first clamping sleeve and thus the clamping force between the nosepiece and the opening in the template when the nosepiece of the work tool should be fixated to the template. According to an aspect of the invention the system may comprise an information carrier configured to feed information to a computer regarding the clamp force between the nosepiece and the surface of the interior wall of a bushing forming the guide opening. The information carrier may be an RFID tag, which comprises a specific identification number connected to a specific receipt, which is stored in a memory of the machine. A RFID reader arranged on the work tool may be coupled to the computer. However, the markings or information carriers may comprise any suitable type of readable ID, such as a RFID tag or chip, a bar code, a colour marking, etc., and can be identified by a reader or sensor on the work tool. Alternatively, each opening in the template may be identified by means of a local orientation system in three di- mensions where the position of the openings may be identified in relation to a number of transmitters and/or reference points located adjacent to or in the vicinity of the template.

Additional objectives, advantages and novel features of the invention will be apparent to one skilled in the art from the following details, and through exercising the invention. While the invention is described below, it should be apparent that the invention may be not limited to the specifically described details. One skilled in the art, having access to the teachings herein, will recognize additional applications, modifications and incorporations in other areas, which are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description of, as examples, preferred embodiments with reference to the enclosed drawings, in which: Fig. 1 illustrates a system according to an embodiment;

Fig. 2 illustrates components of a system according to an embodiment;

Fig. 3 illustrates components of a system according to an embodiment; Figs. 4a-4d illustrate a method according to an embodiment;

Fig. 5 illustrates in a block diagram a system according to an embodiment adapted for a feedback loop controlling a clamp force;

Fig. 6 illustrates a method according to an embodiment in a block diagram; and

Fig. 7 illustrates a method according to an embodiment in a block diagram.

DETAILED DESCRIPTION OF THE DRAWINGS

Hereinafter, embodiments will be described with reference to the accompanying drawings, wherein for the sake of clarity and understanding of the embodiments some details of no importance may be deleted from the drawings. The disclosure is not intended to limit the scope of the enclosed claims in any way.

Fig. 1 illustrates a system 1 for working of a workpiece 2 using a work tool 4, said workpiece 2 may have attached thereto a template 6 with preformed guide openings 8. The guide openings 8 may be located in a pattern corresponding to the positions of holes 10 to be formed in the workpiece 2.

The template 6 may be mounted to the workpiece 2 at a distance therefrom by means of spacers 12 arranged between the template 6 and the workpiece 2. The work tool 4 may comprise a housing 14 in which a spindle 16 may be rotatable arranged. The spindle 16 holds a cutting tool 18 for rotating the cutting tool 18. A nosepiece 20 may be fixedly coupled to the housing 14. The nosepiece 20 may comprise first and second conical clamping sleeves 22, 24, which are axially displaceable in relation to each other. The first conical clamping sleeve 22 may embrace the sec- ond conical clamping sleeve 24. The first conical clamping sleeve 22 may be displaceable along a central axis 26 in relation to the second conical clamping sleeve 24 by means of an electrical machine 28. The electrical machine 28 may be connected to the first conical clamping sleeve 22 via a linkage arrangement 30 The electrical machine 28 may be coupled to a control unit 44 for controlling the expansion of the first conical clamping sleeve 22 and thus the clamping force between the nosepiece 20 and the guide opening 8 in the template 6 when the nosepiece 20 of the work tool 4 should be fixated to the template 6. The electrical machine 28 may be an electrical linear actuator for controlling the clamp force F between the nosepiece 20 and the template 6.

The second conical clamping sleeve 24 of the nosepiece 20 may be provided with a conical envelope surface 32 tapering towards the workpiece 2. The first conical clamping sleeve 22 may be provided with an interior conical surface 34 corresponding with the conical envelope surface 32 of the second conical clamping sleeve 24.

The nosepiece 20 may be configured to fixate or hold the work tool 4 in position relative the guide openings 8. This may be performed by moving the first conical clamp- ing sleeve 22 in a direction from the workpiece 2. By the motion of the first conical clamping sleeve 22 along the second conical clamping sleeve 24 and by the conical surfaces of the sleeves 22, 24 respectively, the first conical clamping sleeve 22 expands and exerts a clamp force F between the nosepiece 20 and an interior wall 54 of the respective guide opening 8 for rigidly holding the work tool 4 in axial position relative the guide opening 8.

The system 1 may comprise means 36 for increasing the coefficient of friction on the surface of the interior wall 54 of the guide opening 8. Also or alternatively the system 1 may comprise means for increasing the coefficient of friction on the envelope sur- face or the outer circumferential surface of the first conical clamping sleeve 22 of the nosepiece 20.

The means for increasing the coefficient of friction on the surface of the template 6 and/or on the surface of the nosepiece 20 may be a surface coating 36. The surface coating 36 may comprise diamonds, such as diamond particles. The surface coating 36 may alternatively comprise other materials or particles that increase the coefficient of friction. The system 1 may further comprise an end effector 38 of a robot arm 40 for positioning the nosepiece 20 in the guide opening 8 of the template 6.

The guide openings 8 may be provided in the template 6 as openings provided with and/or without bushings 55. The bushings 55 may be provided with the surface coating 36 for increasing the coefficient of friction. The surface coating 36 may comprise diamonds, such as diamond particles. The surface coating 36 may alternatively comprise other materials or particles that increase the coefficient of friction. The interior wall 54 of the bushings 55 may be provided with the surface coating 36 for increasing the coefficient of friction. Also, the bushings 55 may be made of a material with an increased coefficient of friction.

The system 1 may comprise an information carrier 42 configured to feed information to a control unit 44 regarding the coefficient of friction on the surface of the interior wall 54 of a bushing forming the guide opening 8.

The information carrier 42 may be an RFID tag. An information carrier reader 46, such as an RFID reader arranged on the work tool 4 may read information sent by the RFID tag. The reader 46 may be coupled to the control unit 44. However, the markings or information carrier 42 may comprise any suitable type of readable ID, such as a RFID tag or chip, a bar code, a colour marking, etc., and can be identified by a reader 46 or sensor on the work tool 4. Alternatively, each guide opening 8 in the template 6 may be identified by means of a local orientation system (not shown) in three dimensions where the position of the openings may be identified in relation to a number of transmitters and/or reference points located adjacent to or in the vicinity of the template 6.

Furthermore, the system 1 may comprise a sensor 48 configured to detect the clamp force F. The sensor 48 may be a strain gauge sensor 48. The sensor 48 may be mounted to the housing 14 and may be configured to measure the clamp force F between the nosepiece 20 and the template 6. The sensor 48 may be coupled to the control unit 44 for controlling the power to the electrical machine 28, so the electrical machine 28 exerts a sufficient force on the first conical clamping sleeve 22. As a result, a robust and accurate controllable system 1 and method may be achieved, which also is able to manage high axial forces which may affect the work tool 4 and cutting tool 18 during the hole cutting process. Fig. 2 illustrates components of a system 1 according to an embodiment. The system 1 may be configured for working of a workpiece 2 using a work tool 4. Guide openings 8 of a template 6 may be located in a pattern corresponding to the positions of holes 10 to be formed in the workpiece 2. The work tool 4 may comprise a housing 14 in which a spindle 16 may be rotatable arranged.

The first conical clamping sleeve 22 may be slidingly arranged around the second conical clamping sleeve 24. The second conical clamping sleeve 24 may be attached to the housing 14. The first conical clamping sleeve 22 may be configured to be moved along the central axis 26 by means of the electrical machine 28 coupled to the control unit 44. The electrical machine 28 may be an electrical linear drive motor which drives a drive rod 50. The drive rod 50 may be coupled to the linkage arrangement 30 which may be pivotable arranged at the housing 14. The linkage arrangement 30 may in turn be coupled to the first conical clamping sleeve 22. By operating the electrical machine 28 the first conical clamping sleeve 22 may be moved along the nosepiece 20 in a controlled manner and with a controlled force. The electrical machine 28 may respond to rapid changes in torque and speed from the work tool 4.

The second conical clamping sleeve 24 of the nosepiece 20 may be provided with a conical envelope surface 32. The first conical clamping sleeve 22 may be provided with an interior conical surface 34 interacting with the conical envelope surface 32 of the second conical clamping sleeve 24 when fixating the work tool 4 in the guide openings 8.

An interior wall 54 of the guide opening 8 may be provided with a material configured to increase the coefficient of friction on the surface of the guide opening 8. Such material that increases the coefficient of friction may overcome the problems of prior art and may be used for a work tool 4 which applying high axial forces acting upon the work tool 4. The material of the interior wall 54 may be applied as a surface coating 36 on the wall 54. Such a system 1 may also be cost-effective. By the system 1 the work tool 4 can be held firmly in position relative the template 6 even if high axial forces are due when forming the hole 10 in the workpiece 2.

Fig. 3 illustrates components of a system 1 according to an embodiment. The first conical clamping sleeve 22 may be slidingly arranged around the second conical clamping sleeve 24 which may be attached to the housing 14 of the work tool 4 and may be configured to be moved along the central axis 26 by means of the electrical machine 28 which may move the first conical clamping sleeve 22 directly via a drive rod 50.

Figs. 4a-4d illustrate a method according to an embodiment. The method may use the work tool 4 for working of the workpiece 2. The template 6 may be provided with the guide openings 8 which may be located in a pattern on the template 6, corresponding to the positions of holes 10 that may be formed in the workpiece 2.

The nosepiece 20 of the work tool 4 may be configured for fixating the work tool 4 in the guide openings 8 by exerting a clamp force F between the nosepiece 20 and an interior wall 54 of the respective guide opening 8. A cutting tool 18 may be arranged in the work tool 4.

The coefficient of friction on the surface of the interior wall 54 of the guide opening 8 may be increased by providing a friction enhancing surface coating 36 on the interior wall 54 of the guide opening 8 as shown in Fig. 4a. The position of an end portion 56 of the cutting tool 18 may be determined by a control unit 44 in relation to a reference line 60 extending in a plane defined by an outer end 58 of the nosepiece 20. The nosepiece 20 may be held in position relative the template 6 and thus also the workpiece 2 during machining by means of the clamping force between the nosepiece 20 and interial wall 54 of the opening in the template 6. Due to the axial forces that may occur on the work tool 4 during machining the clamping force between the nosepiece 20 and interial wall 54 of the opening in the template 6 may be accurately controlled by the power to the electrical machine 28. In Fig. 4b is shown positioning of the nosepiece 20 in one guide opening 8. The outer end 58 of the nosepiece 20 is positioned in contact with the workpiece 2. The reference line 60 coincides with the surface of the workpiece 2. Fig. 4c illustrates an electrical machine 28 which may be mechanically coupled to the first conical clamping sleeve 22. The first conical clamping sleeve 22 may be moved in a direction along the central axis 26 and in a direction from the workpiece 2. The first conical clamping sleeve 22 will expand due to the conical shape of the conical surfaces of the sleeves 22, 24 and the first conical clamping sleeve 22 may exert a clamp force F on the inner wall 54 of the guide opening 8 of the template 6 so that the nosepiece 20 may be secured to the template 6.

In Fig. 4d machining of the workpiece 2 by means of the cutting tool 18 is shown. The position of the end portion 56 of the cutting tool 18 may be determined by the control unit 44 and set in relation to the outer end 58 of the nosepiece 20. By means of the friction enhancing surface coating 36 of the guide opening 8 a rigid clamping of the nosepiece 20 to the template 6 may be achieved. Thus, high axial forces that may result from the cutting tool 18 during the hole making process in the workpiece 2 may not move the nosepiece 20 axially in relation to the template 6. Finished machining of the workpiece 2 at one guide opening 8 involves repositioning of the nosepiece 20 to another guide opening 8 in a repeatedly manner.

Fig. 5 illustrates a block diagram according to a fifth example. The control unit 44 of the system 1 may be configured to execute a feedback loop for controlling the clamp force F.

The sensor 48 may be configured to detect the clamp force F. The sensor 48 may be a strain gauge sensor 48 that may be arranged at a housing 14 of the work tool 4 and coupled to the control unit 44. The control unit 44 may be fed with an input signal 62 regarding a desired clamp force value Fd depending upon actual operation of the work tool 4. This input signal may be an empirical value or a calculated value. The control unit 44 commands the electrical machine 28 to adjust the clamp force F by moving the first conical clamping sleeve 22 along the second conical clamping sleeve 24 of the nosepiece 20 in the direction of the central axis 26. The electrical machine 28 may move the first conical clamping sleeve 22 to a clamping position determined by the desired clamp force value Fd.

The actual value of the clamp force Fa of the first conical clamping sleeve 22 in the clamping position i.e. when the nosepiece 20 being clamped to the interior wall 54 of the guide opening 8 of the template 6, may be measured by means of the sensor 48.

The actual clamp force value Fa may be compared with the desired clamp force value by means of the control unit 44. If the sensor 48 detects that the clamp force value may be insufficient, the control unit 44 may control the electrical machine 28 to move the first conical clamping sleeve 22 a well-defined distance along the second conical clamping sleeve 24 for achieving a stronger clamp force. In such way a robust and with high accuracy controllable system 1 and method may be achieved, which also may be able to manage high axial forces that affect the work tool 4 by the cutting tool 18.

Fig. 6 illustrates a method according to an embodiment shown in a block diagram, and illustrates an exemplary method for operating a system 1 configured for working of a workpiece 2 using a work tool 4.

The method starts in Step 601 . In Step 602 there is provided a method for operating a system 1 configured for working of a workpiece 2 using a work tool 4, said work- piece 2 having attached thereto a template 6 with preformed guide openings 8 located in a pattern corresponding to the positions of holes 10 to be formed in the workpiece 2, said work tool 4 is provided with a nosepiece 20 configured for fixating the work tool 4 relative the guide openings 8 by exerting a clamp force between the nosepiece 20 and an interior wall 54 of the respective guide opening 8. In Step 603 the method is fulfilled and stopped. The step 602 may comprise the steps of; increasing the coefficient of friction on the surface of said interior wall 54 of the guide open- ing 8 and/or on the surface of the nosepiece 20; positioning the nosepiece 20 in one guide opening 8; working of the workpiece 2; and repositioning the nosepiece 20 to another guide opening 8. Fig. 7 illustrates a method according to an embodiment. The method starts in Step 701. Step 702 includes increasing the coefficient of friction on the surface of said interior wall 54 of the guide opening 8 and/or on the surface of the nosepiece 20 by means of a surface coating 36. Step 703 includes determining a desired value of the clamp force for fixating the work tool 4 relative the guide opening 8. Step 704 involves positioning the nosepiece 20 in one guide opening 8 by means of a robot apparatus. Step 705 comprises controlling the clamp force between the nosepiece 20 and the template 6, wherein the clamp force is controlled by means of an electrical machine 28, wherein an actual value of the clamp force is detected and compared with the desired value by a loop execution. Step 706 comprises working of the work- piece 2, wherein a hole-cutting process may be performed in the workpiece 2. Step

707 comprises repositioning of the nosepiece 20 to another guide opening 8. Step

708 comprises that the step of increasing the coefficient of friction on the surface of said interior wall 54 of the guide opening 8 includes providing a bushing 55 having said interior wall 54 and which bushing 55 may be stored in a memory regarding the clamp force between the nosepiece 20 and the surface of the interior wall of a bushing forming the guide opening 8. In Step 709 the method is fulfilled and stopped.

The system 1 may comprise a control unit 44 including a computer program P for carrying out the method according to the invention, in which a software algorithm may provide said calculations about the work tool 4 operation.

The computer program P and a computer program product may be provided for performing the method steps. The computer program P may comprise a program code for performing the method steps according to the embodiments as mentioned herein, when said computer program P is run on a computer. The computer program product may comprise a program code stored on a, by a computer readable media for performing the method steps according to the embodiments as mentioned herein, when said computer program P is run on the computer.

Alternatively, the computer program product may be directly storable in an internal memory into the computer, comprising a computer program P for performing the method steps according to the embodiments, when said computer program P is run on the computer. The computer program P may comprise a program code for performing the steps of Fig. 6. The computer program P may comprise a program code for performing the steps of Fig. 7.

The foregoing description of the preferred embodiments has been furnished for illustrative and descriptive purposes. It is not intended to be exhaustive, or to limit the embodiments to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order to best explicate principles and practical applications, and to thereby enable one skilled in the art to understand the embodiments in terms of its various embodiments and with the various modifications that are applicable to its in- tended use. The components and features specified above may, within the framework of the embodiments, be combined between different embodiments specified.