TECHNICAL FIELD The invention relates to a control arrangement for a nosepiece of a work tool and a method 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 work 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 pro- duced.

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 used. 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 ampli- tude. Such a special hole making apparatus may also use the orbital drilling tech- nique. 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 apparatus uses a nosepiece, which may comprise a clamp- ing means and a cutting tool. The nosepiece is configured to be positioned in a tern- plate mounted at the workpiece. 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 therefore be clamped to the template in the best manner possible for holding the nosepiece in position relative the plane of the template. A conical clamping sleeve slidingly arranged on the nosepiece is typi- cally used to clamp the nosepiece to the template. The clamping force may be achieved by displacing the clamping sleeve, such that it expands.

The documents US6872036 B2, EP 0761351 B1 , US 20080145160 A1 and US 5482411 A disclose different types of drilling machines, which may use a template. The template may comprise a sleeve positioned in the opening of the template for guiding a nosepiece of the drilling apparatus.

SUMMARY OF THE INVENTION Despite known prior art, there is still a need to further develop a control arrangement for a nosepiece of a work tool, which overcomes or at least alleviates problems of prior art.

Hence, an object of the invention is to develop a control arrangement for a nosepiece of a work tool, which control arrangement enables efficient and reliable displacement of a clamping sleeve of the nosepiece for clamping the nosepiece to a template while working a workpiece. Another object of the invention may be to achieve a control ar- rangement for a nosepiece of a work tool, which is compact and has a lower weight. Another object of the invention is to achieve a method for working a workpiece by us- ing a work tool, which method enables efficient and reliable displacement of a clamp- ing sleeve of the nosepiece for clamping the nosepiece to a template.

The herein mentioned objects may be achieved by the above-mentioned control ar- rangement and method according to the appending claims.

According to an aspect of the present disclosure, a control arrangement for a nose- piece of a work tool is provided. The control arrangement comprises: an actuator de- vice; and a linkage arrangement connected to the actuator device, wherein the link- age arrangement comprises a first linkage set with a plurality of link elements, con- nected to a clamping sleeve of the nosepiece, such that movement of the actuator device in its axial direction results in a displacement of the clamping sleeve in its ax- ial direction, the first linkage set comprising a first link element and a second link ele- ment pivotally connected to each other at a first joint forming a knee joint, the first link element further being pivotally connected to a first fixed point on the work tool, wherein the first joint between the first link element and the second link element is connected with the actuator device, so that a linear movement of the first joint trav- erse the axial direction of the actuator device is allowed. Thus, movement of the ac- tuator device in the axial direction of the actuator device results in a displacement of the clamping sleeve in the axial direction of the clamping sleeve

The work tool may be configured for working a workpiece using a template attached to the workpiece. The work tool may apply, and be subject to, high axial forces when working the workpiece. The template may comprise 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 comprise 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. This way, the work tool can be held firmly in position relative the template even when high axial forces are applied for working the workpiece. The nosepiece comprises a clamping sleeve movably ar- ranged on the nosepiece. The clamping sleeve may be configured to be moved along the central axis of the work tool by means of the control arrangement. The nosepiece may further comprise a second sleeve, whereby the clamping sleeve surrounds the second sleeve. The clamping sleeve and the second sleeve may be conical and the clamping sleeve may be displaceable in relation to the second sleeve by means of the control arrangement. The clamping sleeve may be moveable between a first posi- tion and a second position, in which second position the clamping sleeve is displaced in axial direction in relation to the second sleeve. In the first position, the clamping sleeve is in a normal position. In the first position, the clamping sleeve is closer to the workpiece than in the second position. In the displaced second position, the clamping sleeve is expanded as a result of the conical shape of both sleeves. The clamping sleeve may thus be expandable. When the clamping sleeve is expanded, it exerts a clamping force on the template. The clamping force is radially directed in relation to the clamping sleeve. Thus, by controlling the expansion of the clamping sleeve the clamping force between the nosepiece and the template can be controlled. By means of the control arrangement according to the present disclosure, the clamp- ing sleeve may be displaced and thereby expanded in an efficient and reliable way. The linkage arrangement comprising a knee joint enables a power amplification from the actuator device to the clamping sleeve, which means that the clamping sleeve can be displaced by means of a less power from the actuator device. The actuator device can thereby be smaller and more compact, which also reduces the weight of the work tool. Also, the clamping force may be very accurately controlled.

The actuator device may comprise a moveable rod and a linear actuator connected to the rod, wherein the first joint is connected with the moveable rod. Thus, by mov- ing the rod, the first joint between the first link element and the second link element is moved and the clamping sleeve is thereby displaced. The rod is moved by means of the linear actuator. A control unit may be arranged in communication with the linear actuator. The control unit may thereby be configured to control the linear actuator, such that the rod is moved.

According to an example, the linear actuator comprises a pneumatic cylinder and the rod is a piston rod of a piston moveably arranged in the cylinder. The first joint is thus connected with the piston rod. The control unit may be configured to control the pneumatic pressure inside the cylinder, and thereby control the movement of the pis- ton rod. According to another example, the linear actuator comprises an electrical machine connected to the rod. The control unit may control the electrical machine to move the rod and thereby control the clamping force between the nosepiece and the template. The linkage arrangement of the control arrangement may be configured, such that an extracted position of the moveable rod corresponds to the first position of the clamp- ing sleeve and a retracted position of the moveable rod corresponds to the second position of the clamping sleeve. As previously described, the clamping sleeve is ex- panded in the second position. In the second position, the clamping sleeve is dis- placed away from the workpiece. Alternatively, the linkage arrangement may be con- figured, such that an extracted position of the moveable rod corresponds to the sec- ond position of the clamping sleeve and a retracted position of the moveable rod cor- responds to the first position of the clamping sleeve.

The first joint between the first link element and the second link element may be con- nected with the actuator device, so that a linear movement of the first joint, traverse the axial direction of the actuator device, is allowed. According to an example, the first joint is arranged in a slot in the moveable rod, the slot allowing linear movement of the first joint in a direction traverse the axial direction of the rod. The slot in the rod may thus extend in a longitudinal direction perpendicular to the axial direction of the rod. When the rod is moved in the axial direction the first joint is moved in the axial direction and by means of the slot, the first joint is allowed to also move in a direction perpendicular to the axial direction. The linear movement traverse the axial move- ment will affect the rest of the first linkage set, such that the clamping sleeve is dis- placed.

Alternatively, the first link element and the second link element are connected to a third link element at the first joint, wherein the third link element is pivotally connected to the actuator device to allow linear movement of the first joint in a direction traverse the axial direction of the actuator device. The third link element may thus be pivotally connected to the moveable rod of the actuator device at one end and be pivotally connected to the first link element and the second link element at the second end. When the third link element pivots in relation to the actuator device, the first joint will move linearly traverse to the axial direction of the actuator device.

The first link element and the second link element have similar lengths. The first link element and the second link element may thus form a triangle with a base being an imaginary line extending through the first fixed point and a second end of the second link element, wherein the height of the triangle extends between the base and the first joint and the height varies depending on the movement of the actuator device. The height of the triangle may be higher when the moveable rod is in an extracted position than when the rod is in a retracted position. Thus, the top angle of the trian- gle may be smaller when the rod is in an extracted position than when the rod is in a retracted position. The base of the triangle extends between the first fixed point and the end of the second link element being furthest away from the rod. The length of the base of the triangle may thus vary depending on the movement of the actuator device as the top angle changes. The length of the base of the triangle may thus vary depending on the position of the moveable rod. The higher the height of the triangle, the shorter the base. According to an example, by controlling the actuator device, such that the rod is re- tracted, the base of the triangle becomes longer and since the first link element is connected to the first fixed point the first joint will move traverse the axial direction. The second end of the second link element will thereby be moved perpendicularly to the axial direction and will affect the rest of the first linkage set, such that it displaces the clamping sleeve.

The first linkage set may further comprise a fourth link element having a first leverage arm and a second leverage arm, wherein the fourth link element is pivotally con- nected to a second fixed point on the work tool and to the second link element. The second leverage arm may be arranged essentially perpendicularly to the first lever- age arm. The fourth link element may thus be essentially L-shaped. The fourth link element may be connected to the second fixed point at the corner area connecting the first and second leverage arm. A linear movement of the first joint will make the fourth link element pivot about the second fixed point. The first linkage set may also comprise a fifth link element connected to the clamping sleeve of the nosepiece and to the fourth link element. When the actuator device is moved in axial direction, the first joint, and thus the second link element, is moved traverse the axial direction of the actuator device. The fourth link element will thereby pivot about the second fixed point and affect the fifth link element, which thereby displaces the clamping sleeve.

The axial direction of the actuator device may be parallel with the axial direction of the clamping sleeve. In this example, movement of the actuator device in a first direc- tion will displace the clamping sleeve in the same first direction. Thus, when holding the work tool with the nosepiece vertically, movement of the actuator device upwards will displace the clamping sleeve upwards to the second position where it is ex- panded.

According to an example, the linkage arrangement comprises a second linkage set identical to the first linkage set, wherein the first linkage set and the second linkage set are symmetrically arranged on opposite sides of the work tool. This way, the sta- bility is increased, and double power amplification is achieved.

According to another aspect of the present disclosure, a work tool for working a work- piece is provided. Said workpiece has 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 is provided with a nosepiece comprising a clamping sleeve 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 work tool further comprises a control arrangement for the nose- piece as disclosed herein. The work tool may be a drilling machine comprising a ro- tary cutting tool or it may be an orbital drilling apparatus.

According to an example, the work tool comprises a reader configured for reading in- formation from an information carrier on the template. Such information carrier may be configured to feed information to a control device via the reader regarding the clamp force between the nosepiece and the surface of the interior wall of 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 control device. The reader of the work tool may thus be an RFID reader. Flow- ever, the markings or information carriers may comprise any suitable type of reada- ble ID, such as a RFID tag or chip, a bar code, a colour marking, etc., and can be identified by a reader on the work tool. Alternatively, each opening in the template may be identified by means of a local orientation system 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.

According to yet another aspect of the present disclosure, a method, performed by a control device, for working a workpiece by using a work tool as disclosed herein is provided. The work tool thus comprises a nosepiece comprising a clamping sleeve configured for fixating the work tool relative guide openings in a template by exerting a clamp force between the nosepiece and an interior wall of the respective guide opening. The work tool further comprises a control arrangement for the nosepiece as disclosed herein. The method comprises: controlling the clamp force between the nosepiece and the template by means of the control arrangement; and working the workpiece. The method is performed by the control device. The control device may be implemented as a separate entity or distributed in two or more physical entities. The control device may comprise the control unit of the control arrangement. The control device may comprise one or more computers. The control device may thus be implemented or realised by the control device comprising a processor and a memory, the memory comprising instructions, which when executed by the processor causes the control device to perform the herein disclosed method steps. The method may comprise a step of positioning the nosepiece in a guide opening be- fore controlling the clamp force. The step of positioning the nosepiece in a guide opening may comprise controlling a robot arm to position the nosepiece in a guide opening. 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. Alternatively, the work tool is positioned with the nosepiece in a guide opening manually by an op- erator. Thus, the step of controlling the clamp force may be performed when the nosepiece of a work tool is positioned in a guide opening.

The step of controlling the clamp force may comprise detecting an actual value of the clamp force and comparing the actual value with a desired value by a loop execution. The clamp force may thus be adapted to the desired value. The desired value of the clamp force may be a predetermined value or a value depending on the axial forces required to work the workpiece. Thus, the desired value may be higher with higher axial forces. 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 execution, the work tool may be prevented to move in relation to the template during the working process. Controlling the clamp force may also comprise controlling the actuator device of the control arrangement. By controlling the actuator device, such that the moveable rod is moved and the linkage arrangement displaces the clamping sleeve, the clamping sleeve may be expanded and the clamping force is thereby controlled.

The work tool may be a drilling machine comprising a rotary cutting tool, wherein the step of working the workpiece comprises a hole-cutting process performed in the workpiece. 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 inven- tion. 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 schematically illustrates a work tool according to an embodiment;

Fig. 2a-b schematically illustrates control arrangements according to different embod- iments;

Fig. 3 schematically illustrates a control arrangement according to an embodiment;

Figs. 4a-c schematically illustrate different views of a work tool according to an em- bodiment;

Fig. 5 illustrates a diagram associated with a control arrangement according to an embodiment; and Fig. 6 illustrates a block diagram of a method according to an embodiment.

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 schematically illustrates a work tool 1 for working of a workpiece 2. The work- piece 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 1 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 corn- prise a clamping sleeve 22 and a second sleeve 24, which are conical and axially displaceable in relation to each other. The clamping sleeve 22 may circumferentially surround the second sleeve 24. The second sleeve 24 may be attached to the hous- ing 14. The second sleeve 24 of the nosepiece 20 may be provided with a conical en- velope surface 32 tapering towards the workpiece 2. The clamping sleeve 22 may be provided with an interior conical surface 34 corresponding to the conical envelope surface 32 of the second sleeve 24.

The nosepiece 20 may be configured to fixate or hold the work tool 1 in position rela- tive the guide openings 8. This may be performed by moving the clamping sleeve 22 in a direction away from the workpiece 2. The clamping sleeve 22 may be displacea- ble along a central axis 26 in relation to the second sleeve 24 by means of a control arrangement 100 of the work tool 1. The control arrangement 100 may comprise a control unit 44 configured to control the displacement of the clamping sleeve 22 in re- lation to the second sleeve 24. When the clamping sleeve 22 is displaced in direction away from the workpiece 2, the clamping sleeve 22 will expand due to the conical surfaces of the sleeves 22, 24. The clamping sleeve 22 will thereby exert a clamping force between the nosepiece 20 and an interior wall 54 of the guide opening 8 in the template 6. The control unit 44 may be configured to control the expansion of the clamping sleeve 22 and thus the clamping force between the nosepiece 20 and the guide opening 8 in the template 6. The control arrangement 100 will be further de- scribed in Figure 2a-b, Figure 3 and Figure 4.

The work tool 1 may be maneuvered by an end effector 38 of a robot arm 40 for posi- tioning the nosepiece 20 in the guide opening 8 of the template 6.

An information carrier 42 may be arranged on the template 6. The information carrier 42 may be an RFID tag. The work tool 1 may comprise an information carrier reader 46, such as an RFID reader configured to read information sent by the information carrier. The reader 46 may be coupled to the control unit 44. Flowever, 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. Furthermore, the work tool 1 may comprise a sensor 48 configured to detect the clamp force exerted by the clamping sleeve 22. 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 between the nosepiece 20 and the template 6. The sensor 48 may be connected to the control unit 44. The control unit 44 may thereby be configured to control the control arrangement 100 to achieve a desired clamping force, based on the actual clamping force.

The control unit 44 may include a computer program P for carrying out the method as disclosed in Figure 6, in which a software algorithm may provide said calculations. The computer program P and a computer program product may be provided for per- forming 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 per- forming the method steps according to the embodiments as mentioned herein, when said computer program P is run on the computer. Alternatively, the computer pro- gram product may be directly storable in an internal memory into the computer, corn- prising a computer program P for performing the method steps according to the em- bodiments, when said computer program P is run on the computer.

Figure 2a and 2b schematically illustrates control arrangements 100 for a nosepiece 20 of a work tool 1 according to different embodiments. For clarity, only the clamping sleeve 22 of the nosepiece 20 and the work tool 1 is shown in the figures. The control arrangements 100 in these figures are thus each comprised in a work tool 1 as dis- closed in Figure 1. The control arrangement 100 comprises: an actuator device 110; and a linkage arrangement 120 connected to the actuator device 110. The linkage ar- rangement 120 comprises a first linkage set 120’ with a plurality of link elements, connected to the clamping sleeve 22 of the nosepiece 20, such that movement of the actuator device 110 in its axial direction results in a displacement of the clamping sleeve 22 in its axial direction. The axial direction of the clamping sleeve 22 may be along the central axis 26. Movement in the axial direction of the actuator device 110 is a movement along an axis 112 of the actuator device 110. The linkage arrange- ment 120 may be arranged at the housing 14 of the work tool 1.

The first linkage set 120’ comprises a first link element 122 and a second link ele- ment 124 pivotally connected to each other at a first joint J1 , forming a knee joint.

The first link element 122 is further pivotally connected to a first fixed point FP1 on the work tool 1. The first joint J1 between the first link element 122 and the second link element 124 is connected with the actuator device 110, so that a linear move- ment of the first joint J1 traverse the axial direction of the actuator device 110 is al- lowed. The actuator device 110 may comprise a moveable rod 114 and a linear actuator 116 connected to the rod 114, wherein the first joint J1 is connected with the moveable rod 114. The rod 114 is moved along the axis 112 by means of the linear actuator 116. The control unit 44 as disclosed in Figure 1 may be arranged in communication with the linear actuator 116. The control unit 44 may thereby be configured to control the linear actuator 116, such that the rod 114 is moved.

The first link element 122 and the second link element 124 have similar lengths A. The first link element 122 and the second link element 124 may thus form a triangle with a base 2C being an imaginary line extending through the first fixed point FP1 and a second end 124” of the second link element 124. The height B of the triangle extends between the base 2C and the first joint J1 and the height B varies depending on the movement of the moveable rod 114. The length of the base 2C of the triangle also varies depending on the movement/position of the moveable rod 114. The higher the height B of the triangle, the shorter the base 2C.

Figure 2a illustrates an embodiment where the linear actuator 116 comprises a pneu- matic cylinder 116 and the rod 114 is a piston rod 114 of a piston moveably arranged in the cylinder 116. The first joint J1 is thus connected with the piston rod 114. The control unit 44 may be configured to control the pneumatic pressure inside the cylin- der 116, and thereby control the movement of the piston rod 114. Figure 2b illus- trates an embodiment where the linear actuator 116 comprises an electrical machine 116 connected to the moveable rod 114. The control unit 44 may be configured to control the electrical machine 116 to drive the rod 114 and thereby control the clamp- ing force between the nosepiece 20 and the template 6.

The first link element 122 and the second link element 124 are connected to a third link element 128 at the first joint J1. The first link element 122 and the second link el- ement 124 may be connected to a first end of the third link element 128. The third link element 128 is, at another end of the third link element 128, pivotally connected to the rod 114 to allow linear movement of the first joint J1 in a direction traverse the axial direction of the actuator device 110. The first linkage set 120’ may further corn- prise a fourth link element 130 having a first leverage arm E and a second leverage arm D. The fourth link element 130 is pivotally connected to a second fixed point FP2 on the work tool 1 and to the second link element 124. The second leverage arm D may be arranged essentially perpendicularly to the first leverage arm E. The fourth link element 130 may be pivotally connected to the second link element 124 at a sec- ond joint J2. The first linkage set 120’ may also comprise a fifth link element 132 con- nected to the clamping sleeve 22 of the nosepiece 20 and to the fourth link element 130. The fifth link element 132 and the fourth link element 130 may be pivotally con- nected to each other at a third joint J3.

The axial direction of the actuator device 110 is parallel with the axial direction of clamping sleeve 22. Thus, the central axis 26 of the clamping sleeve 22 and the axis 112 of the actuator device 110 may be parallel to each other. In this example, move- ment of the rod 114 upwards in the figure will displace the clamping sleeve 22 in the same upwards direction. The clamping sleeve 22 will thus be in a second (displaced and expanded) position when the rod 114 is in a retracted position. When the rod 114 is moved upwards in the axial direction, the third link element 128 and thus the first joint J1 is moved upwards. Also, since the first link element 122 is connected to the first fixed point FP1 , the third link element 128 will pivot slightly to the left in the fig- ure, whereby the first joint J1 and the second link element 124 are moved traverse the axial direction of the actuator device 110. The second joint J2 will thus move, such that the fourth link element 130 pivots about the second fixed point FP2 to the right in the figure, and move the fifth link element 132 upwards, which thereby dis- places the clamping sleeve 22 axially upwards. The force F provided by the control arrangement 100 for displacing the clamping sleeve 22 axially upwards is herein il- lustrated as an arrow.

Figure 3 schematically illustrates a control arrangement 100 for a nosepiece 20 of a work tool 1 according to an embodiment. For clarity, only the clamping sleeve 22 of the nosepiece 20 and the work tool 1 is shown in the figure. The control arrange- ments 100 in this figure is thus comprised in a work tool 1 as disclosed in Figure 1. The control arrangement 100 is configured as the control arrangement in Figure 2a with the difference that the first joint J1 is arranged in a slot 118 in the moveable rod 114. The first link element 122 and the second link element 124 are thus movably connected to the rod 114. The slot 118 allows linear movement of the first joint J1 in a direction traverse the axial direction of the rod 114. Thus, when the rod 114 is moved upwards in the axial direction the first joint J1 is moved upwards and by means of the slot, the first joint J1 is allowed to also move in a direction perpendicu- lar to the axial direction. The linear movement traverse the axial direction will move the second joint J2 to the left in the figure, whereby the fourth link element 130 pivots to the right around the second fixed point FP2. The fifth link element 132 will thereby be lifted upwards and the clamping sleeve 22 will thereby be displaced axially up- wards.

Figure 4a-c illustrates different views of a work tool 1 according to an embodiment. The work tool 1 may be configured as disclosed in Figure 1. The control arrangement 100 may be configured as disclosed in figure 2a or 2b. In figure 4a, the clamping sleeve 22 is shown connected to the fifth link element 132. The first link element 122 is pivotally connected to a first fixed point FP1 on the work tool 1. The first link ele- ment 122 and the second link element 124 are connected to each other and a third link element 128 at the first joint J1 but the first link element 122 is here partly cov- ered by the housing 14. The third link element 128 is pivotally connected to the rod 114. The figure also shows a fourth link element 130 having a first leverage arm E and a second leverage arm D. The fourth link element 130 is pivotally connected to a second fixed point FP2 on the work tool 1 and to the second link element 124. The second leverage arm D is perpendicular to the first leverage arm E and the fourth link element 130 is thus essentially L-shaped. The fourth link element 130 is pivotally connected to the second link element 124 at a second joint J2. The fifth link element 132 and the fourth link element 130 are pivotally connected to each other at a third joint J3.

Figure 4b shows the work tool 1 in Figure 4a in a view seen from the left in the figure. In this view, a fifth link element 132 of a second linkage set 120” of the linkage ar- rangement 120 can be seen. The first linkage set 120’ and the second linkage set 120” are symmetrically arranged on opposite sides of the work tool 1. This way, the stability is increased, and double power amplification is achieved.

Figure 4c shows the work tool 1 in Figure 4a in a view seen from above. The actuator device 110 comprising a pneumatic cylinder 116 or an electrical machine 116 is illus- trated in this figure and it can be seen that the control arrangement 100 does not af- fect the extension of the work tool 1 to the left in the figure. Thus, the control arrange- ment 100 enables a compact work tool 1 and thereby reduces the weight of the work tool 1.

Figure 5 illustrates a diagram associated with a control arrangement according to an embodiment. The diagram will be explained with regard to the control arrangement 100 as disclosed in Figure 2a. The Y-axis in the diagram shows the force F provided by the control arrangement 100 for displacing the clamping sleeve 22 axially away from the workpiece 2. The X-axis shows the extraction/position of the moveable rod 114. Furthest to the right on the X-axis, the rod 114 is in a fully extracted position where no force F by the control arrangement 100 is acting on the clamping sleeve 22 and the clamping sleeve 22 is thus in a normal first position where it is not extended. Thus, the more retracted the rod 114 is, the higher is the force F acting on the clamp- ing sleeve 22. As can be seen in the diagram, the force F increases exponentially as the rod 114 is retracted. It is to be understood that the values in the diagram are only an example and the values depend on the configuration of the link arrangement 120, the configuration of the rod 114 and the air pressure in the pneumatic cylinder 116. By means of the linkage arrangement 120 of the control arrangement 100, an ampli- fier is achieved. Thus, a force applied on the moveable rod 114 will be amplified by means of the linkage arrangement 120, so that the force F acting on the clamping sleeve 22 becomes larger. From the triangle formed by the first and second link ele- ments 122, 124 in Figure 2a two smaller right-angled triangles comprising one of the link elements 122, 124 can be formed, whereby the following expression E1 is achieved:

A ² = c ² + B ² C = /A ² - B ² [E1 ] where A is the length of the first link element 122/the second link element 124, B is the height of the triangle and thus the distance between the first joint J1 and the im- aginary line crossing the first fixed point FP1 and the second joint J2; and C is the length of the base of the right-angled triangle, the base being half the length of the imaginary line 2C extending between the first fixed point FP1 and the second joint J2. From this expression, it is given that the length C is dependent of the height B. Since the height B changes depending on the movement of the moveable rod 114, the dif- ference in length between A and C will also change depending on the movement of the moveable rod 114. By dividing B with A-C, the relationship between the change of B in relation to the change of difference between A and C is achieved. The linkage arrangement 120 forming two right-angled triangles gives the relationship B/(2*(A- C)). This relationship is variable and when B approaches zero, the change of differ- ence between A and C is infinitely small. In this case, the amplification of a force ap- plied to change B is maximal. Thus, when A has a fixed length and the height B is changed, the amplifying ratio B = B/(2 * (A-C)) is achieved. Flowever, this amplifica- tion from the knee joint should be halved since half of the force is directed to the first fixed point FP1. The amplification from the knee joint acting on the clamping sleeve 22 is thus B/(4 * (A-C)). Developed with the linkage arrangement 120 as disclosed herein using the law of the lever, this is multiplied with E/D which gives the amplifying ratio B= B/(4 * (A-C)) Έ/D. Replacing C with the expression in E1 gives the amplify- ing ratio achieved by means of the linkage arrangement 120 as defined by the equa- tion E2 below

B E

Ratio B = *— [E2]

(X-Vx ² -S ² ) 4 D where A is the length of the first link element 122/the second link element 124; B is the height of the triangle and thus the distance between the first joint J1 and the im- aginary line crossing the first fixed point FP1 and the second joint J2; D is the length of the second leverage arm and E is the length of the first leverage arm of the fourth link element 130.

Fig. 6 illustrates a method, performed by a control device 44, for working a workpiece by using a work tool 1 according to an embodiment. The work tool 1 may be config- ured as disclosed in Figure 1. The work tool 1 thus comprises a nosepiece 20 com- prising a clamping sleeve 22 configured for fixating the work tool 1 relative guide openings 8 in a template 6 by exerting a clamp force between the nosepiece 20 and an interior wall 54 of the respective guide opening 8. The work tool 1 further corn- prises a control arrangement 100 for the nosepiece 20 as disclosed in figure 2a, 2b or 3. The method comprises: controlling s101 the clamp force between the nosepiece 20 and the template 6 by means of the control arrangement 100; and working s102 the workpiece 2. The control device performing the method may be implemented as a separate entity or distributed in two or more physical entities. The control device may comprise the control unit 44 of the control arrangement 100. The control device may comprise one or more computers. The control device may thus be implemented or realised by the control device comprising a processor and a memory, the memory comprising in- structions, which when executed by the processor causes the control device to per- form the herein disclosed method steps.

The method may alternatively comprise the step of, before controlling s101 the clamp force, positioning s103 the nosepiece 20 in a guide opening 8. The step of position- ing s103 the nosepiece 20 in a guide opening 8 may comprise controlling a robot arm 40 to position the nosepiece 20 in a guide opening 8.

The step of controlling s101 the clamp force may comprise detecting an actual value of the clamp force and comparing the actual value with a desired value by a loop ex- ecution. The step of controlling s101 the clamp force may thus comprise determining a desired value of the clamp force for fixating the work tool 1 relative the guide open- ing 8. The desired value of the clamp force may be a predetermined value or a value depending on the axial forces required to work the workpiece 2. Thus, the desired value may be higher with higher axial forces. By detecting the actual value of the clamp force and adapting the clamp force for fixating the work tool 1 relative the guide opening 8 to a desired value of the clamp force by a loop execution, the work tool 1 may be prevented to move in relation to the template 6 during the working pro- cess. Controlling s101 the clamp force may also comprise controlling the actuator device 110 of the control arrangement 100. Controlling the actuator device 110 may corn- prise controlling a linear actuator 116 to move a moveable rod 114. By controlling the actuator device 110, such that the moveable rod 114 is moved and the linkage ar- rangement 120 displaces the clamping sleeve 22, the clamping sleeve 22 may be ex- panded and the clamping force is thereby controlled. The work tool 1 may be a drilling machine comprising a rotary cutting tool 18, wherein the step of working s102 the workpiece 2 comprises a hole-cutting process performed in the workpiece 2.

The foregoing description of the preferred embodiments has been furnished for illus- trative and descriptive purposes. It is not intended to be exhaustive, or to limit the embodiments to the variants described. Many modifications and variations will obvi- ously 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 frame- work of the embodiments, be combined between different embodiments specified. It is thus to be understood that for example the connection between the link arrange- ment and the actuator device as disclosed in Figure 3 may be combined with the ac- tuator device as disclosed in Figure 2b.