ENHANCED METHOD FOR CUTTING PIPES ON A DRILL FLOOR AND TOOL THEREFOR

Abstract

A method is for cutting a tubular structure in the petrochemical industry, using a cutting tool having a non-rotatable cutting element and a reaction member opposite the non-rotatable cutting element. The cutting tool is further configured for carrying out a translational cutting movement through the tubular structure. The method comprises: a) positioning the cutting tool in a first position exterior to the tubular structure; b) squeezing the tubular structure at the first position by activating a partial translational cutting movement of the non-rotatable cutting element to obtain a dented region in the tubular structure; c) positioning the cutting tool in a second position exterior to the tubular structure, wherein the second position is displaced over a predefined distance compared to the first position, and d) cutting the tubular structure at the second position (P2) by activating a full translational cutting movement of the non-rotatable cutting element through the tubular structure.

Claims

1. A cutting tool for cutting a tubular structure at a drill floor of a drilling rig, the cutting tool comprising: a tool body forming at least a portion of an enclosure configured to receive the tubular structure; a non-rotatable cutting element positioned on a first side of the enclosure; and a reaction member opposite to the non-rotatable cutting element across the enclosure, wherein a distance between the non-rotatable cutting element and the reaction member is adjustable to squeeze the tubular structure as the distance between the non-rotatable cutting element and the reaction member decreases, and carry out a translational cutting movement through the tubular structure when the distance between the non-rotatable cutting element and the reaction member decreases to a cutting distance, and wherein the cutting tool is configured to perform a partial translational cutting movement of the non-rotatable cutting element in which the distance between the non-rotatable cutting element and the reaction member does not reach the cutting distance to obtain a dented region in the tubular structure at a first position, and perform a full translational cutting movement of the non-rotatable cutting element in which the distance between the non-rotatable cutting element and the reaction member reaches the cutting distance to cut the tubular structure at a second position.

2. The cutting tool of claim 1, further comprising: an adapter device that covers a cutting edge of the non-rotatable cutting element during the partial translational cutting movement, wherein the cutting edge of the non-rotatable cutting element is relatively sharp, and wherein a leading edge of the adapter device is relatively blunt with respect to the cutting edge of the non-rotatable cutting element.

3. The cutting tool of claim 1, further comprising: a second cutting element mechanically coupled to the reaction member such that a portion of the second cutting element touches a portion of the non-rotatable cutting element during the full translational cutting movement, and does not touch the portion of the non-rotatable cutting element during the partial translational cutting movement.

4. The cutting tool of claim 3, wherein the portion of the second cutting element corresponds to a cutting edge of the second cutting element that is relatively sharp, wherein the cutting tool further comprises: a second adapter device that covers the cutting edge of the second cutting element during the partial translational cutting movement, wherein a leading edge of the second adapter device is relatively blunt with respect to the cutting edge of the second cutting element.

5. The cutting tool of claim 4, wherein the portion of the non-rotational cutting element corresponds to a cutting edge of the non-rotational cutting element that is relatively sharp wherein the cutting tool further comprises: an adapter device that covers the cutting edge of the non-rotatable cutting element during the partial translational cutting movement, wherein the cutting edge of the non-rotatable cutting element is relatively sharp, and wherein a leading edge of the adapter device is relatively blunt with respect to the cutting edge.

6. The cutting tool of claim 1, wherein the reaction member is pivotably mounted to the tool body such that in a closed position the reaction member forms a second portion of the enclosure, and in an open position the reaction member allows the tubular structure to be inserted in the enclosure.

7. The cutting tool of claim 1, further comprising: an adapter having a blunt cutting edge and a receiving portion comprising a first receiving site, a second receiving site, and a third receiving site disposed between the first receiving site and the second receiving site, wherein the receiving portion is configured to cover a cutting edge of the non-rotatable cutting element such that the cutting edge of the non-rotatable cutting element contacts the third receiving site of the adapter, an upper surface of the of the non-rotatable cutting element contacts the first receiving site of the adapter, and a lower surface of the of the non-rotatable cutting element contacts the second receiving site of the adapter, and the blunt cutting edge of the adapter faces the tubular structure when the adapter is covering the cutting edge of the non-rotatable cutting element.

8. The cutting tool of claim 7, wherein the adapter is pivotably mounted to the non-rotatable cutting element such that the adapter pivots between at least a first position in which the adapter does not cover the cutting edge of the non-rotatable cutting element and a second position in which the adapter covers the cutting edge of the non-rotatable cutting element, wherein the adapter is in the first position during the full translational cutting movement, and is in the second position during the partial translational cutting movement.

9. The cutting tool of claim 7, wherein a height of the blunt cutting edge of the adapter along a first direction that is generally parallel to a central axis of the tubular structure is larger than a height of the cutting edge of the non-rotatable cutting element along the first direction, such that the blunt cutting edge of the adapter is relatively blunt with respect to the cutting edge of the non-rotatable cutting element.

10. The cutting tool of claim 1, further comprising: a second cutting element mechanically coupled to the reaction member such that a portion of the second cutting element touches a portion of the non-rotatable cutting element during the full translational cutting movement, and does not touch the portion of the non-rotatable cutting element during the partial translational cutting movement; and a second adapter having a second blunt cutting edge and a second receiving portion comprising a first receiving site, a second receiving site, and a third receiving site disposed between the first receiving site and the second receiving site, wherein the second receiving portion is configured to cover a cutting edge of the second cutting element such that the cutting edge of the second cutting element contacts the third receiving site of the second adapter, an upper surface of the of the second cutting element contacts the first receiving site of the second adapter, and a lower surface of the of the second cutting element contacts the second receiving site of the second adapter, and the second blunt cutting edge faces the tubular structure when the second adapter is covering the cutting edge of the second cutting element.

11. An assembly for cutting a tubular structure at a drill floor of a drilling rig using a translational cutting movement, the assembly comprising: a tool body comprising an enclosure configured to receive the tubular structure; a non-rotatable cutting element coupled to the tool body on a first side of the enclosure; a reaction member coupled to a second cutting element; and a linear actuator coupled to the non-rotatable cutting element, and configured to carry out a translational movement of the non-rotatable cutting element toward a second side of the enclosure, wherein the assembly is configured to perform a partial translational cutting movement of the non-rotatable cutting element with the reaction member in a closed position, the partial translational cutting movement causes a distance between the non-rotatable cutting element and the second cutting element to decrease to a first distance to obtain a dented region in the tubular structure at a first position along the tubular structure, wherein the non-rotatable cutting element does not touch the second cutting element at the first distance, and perform a full translational cutting movement of the non-rotatable cutting element with the reaction member in the closed position at a second position along the tubular structure, the full translational cutting movement causes the distance between the non-rotatable cutting element and the second cutting element to decrease to a second distance that is smaller than the first distance to cut through the tubular structure at the second position along the tubular structure.

12. The assembly of claim 11, further comprising: a first adapter configured to cover a cutting edge of the non-rotatable cutting element during the partial translational cutting movement, the first adapter having a leading edge and a receiving portion configured to receive the non-rotatable cutting element, wherein a cutting edge of the non-rotatable cutting element has a first surface area and the leading edge of the first adapter has a second surface area that is greater than the first surface area such that the leading edge of the first adapter is blunt relative to the cutting edge of the non-rotatable cutting element; and a second adapter configured to cover a cutting edge of the second cutting element during the partial translational cutting movement, the second adapter having a leading edge and a receiving portion configured to receive the second cutting element, wherein a cutting edge of the second cutting element has a third surface area and the leading edge of the second adapter has a fourth surface area that is greater than the third surface area such that the leading edge of the second adapter is blunt relative to the cutting edge of the second cutting element.

13. The assembly of claim 12, wherein the first adapter is pivotably mounted to the non-rotatable cutting element, and the second adapter is pivotably mounted to the second cutting element.

14. The assembly of claim 11, wherein the reaction member is pivotably mounted to the tool body such that in a closed position the reaction member closes the second side of the enclosure, and in an open position the second side of the enclosure is open for allowing receiving of the tubular structure in the enclosure.

15. The assemble of claim 14, wherein the reaction member is coupled to the tool body via a hinge on a first side of the tool body, and is configured to lock to a second side of the tool body that is opposite the enclosure from the first side using a locking mechanism.

16. The assembly of claim 11, wherein the reaction member is configured to maintain a static position with respect to the tool body during the partial translational cutting movement and during the full translational cutting movement.

17. A method for cutting a tubular structure, the method comprising: positioning a cutting tool in a first position exterior to the tubular structure, wherein the cutting tool comprises: a tool body forming at least a portion of an enclosure configured to receive the tubular structure; a non-rotatable cutting element positioned on a first side of the enclosure; and a reaction member opposite to the non-rotatable cutting element across the enclosure; reducing a distance between the non-rotatable cutting element and the reaction member, at the first position, the distance between the non-rotatable cutting element and the reaction member to a first distance, thereby squeezing the tubular structure; increasing the distance between the non-rotatable cutting element and the reaction member after squeezing the tubular structure at the first position, thereby obtaining a dented region in the tubular structure at the first position; positioning the cutting tool in a second position exterior to the tubular structure, wherein the second position is displaced over a predefined distance compared to the first position; and reducing a distance between the non-rotatable cutting element and the reaction member, at the second position, until the distance between the non-rotatable cutting element and the reaction member to a cutting distance, thereby cutting through the tubular structure, wherein the cutting distance is less than the first distance.

18. The method of claim 17, further comprising: covering a cutting edge of the non-rotatable cutting element using a first adapter prior to squeezing the tubular structure at the first position; covering a cutting edge of a second cutting element coupled to the reaction member using a second adapter prior to squeezing the tubular structure at the first position; removing the first adapter from the cutting edge of the non-rotatable cutting element prior to cutting the tubular structure at the second position, thereby uncovering the cutting edge of the non-rotatable cutting element; and removing the second adapter from the cutting edge of the second cutting element prior to cutting the tubular structure at the second position, thereby uncovering the cutting edge of the second cutting element, wherein the cutting distance is less than the first distance by at least a thickness of the first adapter and the second adapter.

19. The method of claim 17, further comprising: pivoting a first side of the reacting member away from the tool body using a hinge on a second side of the reaction member, thereby opening the enclosure; receiving the tubular structure in the enclosure while the enclosure is open; and pivoting the first side of the reacting member toward the tool body using the hinge on the second side of the reaction member, thereby closing the enclosure after receiving the tubular structure.

20. The method of claim 17, wherein the tubular structure comprises a plurality of pipes including a first pipe and a second pipe, the second pipe being disposed within the first pipe, and squeezing the tubular structure includes squeezing the second pipe.

Description

BRIEF INTRODUCTION OF THE DRAWINGS

[0032] In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein:

[0033] FIG. 1a shows a top view of an embodiment of a cutting tool in accordance with the invention with the non-rotatable cutting element retracted;

[0034] FIG. 1b shows a top view of an embodiment of a cutting tool in accordance with the invention with the non-rotatable cutting element partially extended;

[0035] FIGS. 2a-c show a tubular structure comprising a pipe assembly, which may particularly benefit from the invention;

[0036] FIGS. 3a-c show a stage of the method of cutting a tubular structure in accordance with the invention;

[0037] FIGS. 4a-c show a further stage of the method of cutting a tubular structure in accordance with the invention;

[0038] FIGS. 5a-c show a further stage of the method of cutting a tubular structure in accordance with the invention;

[0039] FIGS. 6a-c show a further stage of the method of cutting a tubular structure in accordance with the invention;

[0040] FIG. 7 shows a stage of a method of handling a tubular structure in accordance with the invention;

[0041] FIG. 8 shows a further stage of the method of handling a tubular structure in accordance with the invention;

[0042] FIGS. 9a-b illustrate a first aspect of the invention;

[0043] FIGS. 10a-b illustrate another aspect of the invention;

[0044] FIGS. 11a-b illustrate part of an embodiment of the cutting tool in accordance with the invention, and

[0045] FIGS. 12a-b illustrate another part of an embodiment of the cutting tool in accordance with the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] Various illustrative embodiments of the present subject matter are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0047] The present subject matter will now be described with reference to the attached figures. Various systems, structures and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.

[0048] The figures and description below illustrate embodiments of methods of cutting a tubular structure in the petrochemical industry as well as embodiments of cutting tools, which may be used in such methods.

[0049] FIG. 1a shows a top view of an embodiment of a cutting tool 100 in accordance with the invention with the non-rotatable cutting element retracted. FIG. 1b shows a top view of an embodiment of a cutting tool 100 in accordance with the invention with the non-rotatable cutting element partially extended. The cutting tool 100 may be installed on the drill floor as a mount onto the roughneck (not shown) or as a stand-alone system (not shown), which may be run back and forth (for instance using a rail system) over the Rotary Kelly Bushing (RKB) for each cut. Alternatively, it may be manipulated by means of a crane or manipulator (not shown). Alternatively, the cutting tool 100 may be used at other places.

[0050] FIG. 1a shows a cutting tool 100 with an enclosure 50 for receiving a tubular structure to be cut (not shown). The enclosure 50 is defined by a tool body 110 and a reaction member 140. The cutting tool comprises a linear actuator 120. The linear actuator 120 comprises in this embodiment two hydraulic cylinders, but it may be any other number of hydraulic cylinders or it may be other types of actuators such as jacks. The linear actuator 120 is coupled to a non-rotatable cutting element 130 at first side S1 of the enclosure 50 (shown in FIG. 1b) and configured for carrying out translational cutting movement with said cutting element 135. The reaction member 140 comprises a further cutting element 145 facing the enclosure 50 mounted on a second side S2 opposite to the first side S1, as illustrated. The reaction member 140 in this embodiment is pivotably mounted to the tool body 110 as illustrated. The reaction member 140 may be opened for allowing receiving of the tubular structure in the enclosure 50. In FIG. 1b it is also illustrated that during the extension of the cutting element 135 it is guided on opposing sides by guides 125 in which the cutting element 135 slides. This results in more stable cutting and squeezing.

[0051] In the case of a hydraulic actuator 120 it would typically comprise hydraulic cylinder (not shown) with piston (not shown) and a piston rod (not shown) onto which the cutting element 135 is mounted. In operational use the cutting element 135 will come out and, in the current invention, either squeeze or cut the tubular 1 against the cutting element 145 on the reaction member 140, depending on the length of the stroke of the cutting element 145. In fact FIG. 1b illustrates a possible stroke that may be applied for squeezing the tubular structure without cutting it. It may be observed that the enclosure 50 is smaller but the cutting element 135 does not touch the further cutting element 145.

[0052] The embodiment of the cutting tool of FIGS. 1a and 1b can cut tubular structures up to 36-inch (914 mm), and is able to squeeze and/or cut drill pipes through the tool joints as well as cemented and lined casings without any problems.

[0053] It must be stressed that within the scope of the current claims also other designs and dimensions of the cutting tool are possible, such that the cutting tool is designed for other dimensions of tubular structures. Alternatively, cutting tools may be used which have multiple movable cutting element arranged around the enclosure, i.e. two or four or a different number.

[0054] FIGS. 2a-c show a tubular structure 1 comprising a pipe assembly, which may particularly benefit from the invention. This tubular structure 1 comprises a plurality of pipes that are concentrically placed over each other. In the current example there is an outer pipe 1-1, which may be a conductor in a practical example (or which may be a riser with multiple internal casings in other examples). Inside the conductor 1-1 there is provided a middle pipe 1-2, which may be a casing in a practical example (or which may be a lined casing, a cemented casing, or a cemented lined casing in other examples). Inside the middle pipe 1-2 there is provided an inner pipe 1-3, which may be a production tubing in a practical example (or which may be a drill string, a drill pipe in other examples). Here there are three concentric pipes, but it may also be another number of pipes in practise. In between said concentric pipes there may be cement or other masses. As already discussed before, a problem may occur when such tubular structures 1 are cut and vertically lifted. In such scenario there is a risk that the inner tubes, including any cement, fall out. In the prior art this problem is typically solved with time-consuming pinning processes.

[0055] FIGS. 3a-c show a stage of the method of cutting a tubular structure 1 in accordance with the invention. FIG. 3a shows a top view. FIG. 3b shows a cross-sectional side view. FIG. 3c shows a perspective view. In this stage of the method the cutting tool 100 is positioned at a first position P1. This means that the reaction member 140 is opened first allowing the tubular structure 1 to be inserted in the enclosure 50 as illustrated. In the current example the cutting tool 100 is further provided with a plurality of hoisting connection points 171, which facilitate handling by means of a crane or other type of manipulator (not shown).

[0056] FIGS. 4a-c show a further stage of the method of cutting a tubular structure 1 in accordance with the invention. FIG. 4a shows a top view. FIG. 4b shows a cross-sectional side view. FIG. 4c shows a perspective view. In this stage of the method the cutting tool 100 is used to squeeze the tubular structure 1 at the first position P1 as illustrated. Expressed differently, the cutting element 135 is moved/pushed towards the further cutting element 145, but does not fully reach it, which is referred to in the claims as a partial translational cutting movement. During this squeezing step the tubular structure 1 deforms at forms outward projections 1p as illustrated in FIG. 4a and FIG. 4c.

[0057] FIGS. 5a-c show a further stage of the method of cutting a tubular structure 1 in accordance with the invention. FIG. 5a shows a top view. FIG. 5b shows a cross-sectional side view. FIG. 5c shows a perspective view. In this stage of the method the cutting tool 100 releases the tubular structure 1 and is subsequently moved up to a second position P2 as illustrated, displaced over a predefined distance dp. In a dismantling process of a casing in from a well it is advantageous if the second position P2 is above the first position P1 when the tubular structure 1 is oriented in an upright position. This will be explained later. However, the invention is not limited to this variant of the method. It is important to note that the tubular structure 1 at this stage has a dented region D1 as illustrated.

[0058] FIGS. 6a-c show a further stage of the method of cutting a tubular structure 1 in accordance with the invention. FIG. 6a shows a top view. FIG. 6b shows a cross-sectional side view. FIG. 6c shows a perspective view. In this stage of the method the cutting tool 100 is used to cut the tubular structure 1 at the second location P2 as illustrated. Expressed differently, the cutting element 135 is moved/pushed completely towards the further cutting element 145, and touches it, which is referred to in the claims as a full translational cutting movement.

[0059] FIG. 7 shows a stage of a method of handling a tubular structure 1 in accordance with the invention. In fact this method follows on the method illustrated in FIGS. 3a-6c. The dented region D1 is now clearly visible at the upper section of the remaining tubular structure 1. Now, the tubular structure 1 may be further handled by a slips device 200 as illustrated. The slips device 200 comprises a first part 202 pivotably mounted to a second part 204 as illustrated so as to form a further enclosure that is designed to match the form of the dented region D1. In FIG. 7 the slips device 200 is opened as illustrated so that the tubular structure 1 may be received inside its enclosure.

[0060] FIG. 8 shows a further stage of the method of handling a tubular structure 1 in accordance with the invention. In this stage the slips device 200 is provided around the dented region D1 and closed. The slips device 200 in FIGS. 7 and 8 also comprises respective lifting hooks 206 as illustrated, which allow the slips device 200 to be handled by a hoisting device, crane or manipulator (not shown). In the stage of FIG. 8 the tubular structure 1 possible with a large string of tubular structures underneath may be lifted up in order to allow cutting of the tubular structure 1 at a further position below the first position. In this way the tubular structure 1 may be severed piece by piece by sequentially squeezing, cutting and lifting said tubular structure.

[0061] FIGS. 9a-b illustrate a first aspect of the invention. These figures illustrate what is meant with the earlier discussed dented region D1 of the tubular structure 1 at the first position P1. The outward projections 1p are also clearly illustrated.

[0062] FIGS. 10a-b illustrate another aspect of the invention. These figures illustrate what is meant with the so-called shoulders 199 formed in the dented region D1 as mentioned in the claim. Each dent on each side clearly causes two shoulders 199 opposite to each other as illustrated in FIG. 10b. These shoulders 199 form the parts that is gripped in between by the earlier-discussed slips device 200. FIGS. 10a and 10b also illustrate the cutting region C1 that is located at the earlier-discussed second position P2. At this cutting region C1 the tubular structure 1 is squeezed completely together to get a form similar to these figures.

[0063] FIGS. 11a-b illustrate part of an embodiment of the cutting tool in accordance with the invention. The illustrated part is the non-rotatable cutting element 135, which in FIG. 11a has a sharp cutting 135s, an upper surface 135u, and a lower surface 1351. It has already been mentioned that in principle the cutting tool as disclosed in or similar to the one in WO2017/099607A1 may be used, i.e. a cutting tool with sharp cutting edges. However, the cutting tool in accordance with the current invention may be improved by implementing an adapter 137 as illustrated in FIGS. 11a-b. This adapter 137 is shaped to cover the sharp cutting edge 135s and effectively forms a blunter cutting edge 137b for the cutting element 135. The adapter 137 includes a receiving portion that is shaped to cover the sharp cutting edge 135s and a portion of the non-rotatable cutting element 135, an edge receiving site 137s, an upper receiving site 137u, and a lower receiving site 1371. In operational use, when covering the sharp cutting edge 135s, the sharp cutting edge 135s of the non-rotatable cutting element contacts the edge receiving site 137s, the upper surface 135u contacts the upper receiving site 137u, and the lower surface 135l contacts the lower receiving site 1371. The level of sharpness and the level of bluntness in FIGS. 11a and 11b may vary. It may even be arbitrary what the definition of sharp is in this respect. What is important is that there is at least different levels of sharpness or bluntness for the cutting element 135. The adapter 137 may be provided manually on the cutting element 135 or it may be pivotably mounted to the cutting element 135. The use of the adapter 137 turns the cutting element 135 into a configurable cutting element, wherein the cutting edge may be sharp or blunter depending on the requirements of the stage of the method of the invention.

[0064] FIGS. 12a-b illustrate another part of an embodiment of the cutting tool in accordance with the invention. The illustrated part is the further cutting element 145, which in FIG. 12a has a further sharp cutting 145s, an upper surface 145u, and a lower surface 145l. The cutting tool in accordance with the current invention may be improved by implementing a further adapter 147 as illustrated in FIG. 12b. This further adapter 147 is shaped to cover the further sharp cutting edge 145s and effectively forms a blunter cutting edge 147b for the further cutting element 145. The adapter 147 includes a receiving portion that is shaped to cover the sharp cutting edge 145s and a portion of the further cutting element 145, an edge receiving site 147s, an upper receiving site 147u, and a lower receiving site 147l. In operational use, when covering the sharp cutting edge 145s, the sharp cutting edge 145s of the further cutting element contacts the cutting edge receiving site 147s, the upper surface 145u contacts the upper receiving site 147u, and the lower surface 145l contacts the lower receiving site 147l. The level of sharpness and the level of bluntness in FIGS. 12a and 12b may vary. The definition of sharp may be even arbitrary in this respect. What is important is that there are at least different levels of sharpness or bluntness for the further cutting element 145. The further adapter 147 may be provided manually on the further cutting element 145 or it may be pivotably mounted to the further cutting element 145. The use of the further adapter 147 turns the further cutting element 145 into a configurable cutting element, wherein the cutting edge may be sharp or blunter depending on the requirements of the stage of the method of the invention.

[0065] With reference to FIGS. 11b and 12b it must be noted that these aspects may be conveniently combined such that both cutting edges are configurable in terms of sharpness or bluntness.

[0066] The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different yet equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the method steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the invention. Accordingly, the protection sought herein is as set forth in the claims below.

[0067] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb comprise and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article a or an preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. In the device claims enumerating several means, several of these means may be embodied by one and the same item of hardware.