The invention relates to a method for manufacturing an electrical contact arrangement on an end of a hoisting rope of a hoisting apparatus, and to an electrical contact arrangement on an end of a hoisting rope of a hoisting apparatus and to an arrangement for condition monitoring of a hoisting rope of a hoisting apparatus. Said hoisting apparatus is preferably an elevator for transporting passengers and/or goods.
Hoisting ropes typically include one or several load bearing members that are elongated in the longitudinal direction of the rope, each load bearing member forming a structure that continues unbroken throughout the length of the rope. Load bearing members are the members of the rope which are able to bear together the load exerted on the rope in its longitudinal direction. The load, such as a weight suspended by the rope, causes tension on the load bearing member in the longitudinal direction of the rope, which tension can be transmitted by the load bearing member in question all the way from one end of the rope to the other end of the rope. Ropes may further comprise non-bearing components, such as an elastic coating, which cannot transmit tension in the above described way.
In prior art, such hoisting ropes exist where the load bearing members are embedded in non-conducting coating, such as polymer coating, forming the surface of the hoisting rope and extending between adjacent load bearing members thereby isolating them from each other both mechanically and electrically. For facilitating awareness of condition of the condition of ropes, and thereby for improving safety of the hoisting apparatus, monitoring of the condition of the load bearing members has been proposed. The condition monitoring has been proposed in prior art to be arranged by monitoring electrical parameters of the load bearing members. Such parameters may include resistance for instance. For this purpose, the load bearing members need to be connected electrically to a source of electricity. A drawback has been that there has not been an effective and simple way for providing the electrical connection.
Furthermore, such solutions exist where said load bearing members are in the form of elongated composite members made of composite material comprising reinforcing fibers in polymer matrix. In this type of solutions, establishing the electrical connection has been particularly challenging owing to the fragility of the composite material of the load bearing members.
The object of the invention is to introduce a method for manufacturing an electrical contact arrangement on an end of a hoisting rope of a hoisting apparatus, as well as an electrical contact arrangement on an end of a hoisting rope of a hoisting apparatus, and an arrangement for condition monitoring of a hoisting rope of a hoisting apparatus, and a hoisting apparatus, wherein an electrical contact is provided for load bearing members next to each other in a manner improved in terms of simplicity of structure and ease of implementation. Advantageous embodiments are furthermore presented, inter alia, wherein a contact interface is provided via which electricity is simply conducted into load bearing members. Advantageous embodiments are furthermore presented, inter alia, wherein process steps requiring accuracy can be carried out quickly with excellent quality.
It is brought forward a new method for manufacturing electrical contact arrangement on an end of a hoisting rope of a hoisting apparatus, which hoisting rope comprises a non-conductive coating, and a plurality of adjacent conductive load bearing members for bearing the load exerted on the rope in longitudinal direction thereof embedded in the coating and extending parallel to each other and to the longitudinal direction of the hoisting rope unbroken throughout the length of the rope, the coating forming the surface of the hoisting rope and extending between adjacent load bearing members thereby isolating them from each other (both mechanically and electrically), and in the method a conductive plate element is placed beside the end of the hoisting rope; and the conductive plate element is attached immovably beside the end of the hoisting rope with at least one threaded screw member made of conductive material by screwing the screw member into the hoisting rope such that it extends centrally between load bearing members next to each other, and such that the threads thereof are in contact with both of said load bearing members next to each other, the contact element being thereby brought to be in conductive connection with both of said load bearing members next to each other via said at least one screw member. Hereby, one or more of the above mentioned advantages and/or objectives are achieved. These advantages and/or objectives are further facilitated with the additional preferred features and/or steps described in the following.
In a preferred embodiment, said at least one threaded screw member is screwed to compress with its screw head directly the conductive plate element, or indirectly via only conductive members such as one or more washers.
In a preferred embodiment, said conductive plate element is a contact element that can be directly coupled with another contact element. Thereby, said conductive plate element can serve as a contact interface via which electricity can be conducted into both of said load bearing members.
In a preferred embodiment, in the method said contact element is coupled directly with a contact element of a source of electricity, in particular to a contact element of the source of electricity serving as a positive or negative terminal thereof. Thereby, said conductive plate element can serve as a contact interface via which electricity can be conducted into both of said load bearing members from a source of electricity
In a preferred embodiment, before said placing and screwing, a hole is pre-drilled into the coating which hole extends centrally between load bearing members next to each other, and in said screwing the screw member is screwed into the pre-drilled hole.
In a preferred embodiment, before said pre-drilling, the rope is mounted on a jig comprising a plurality of stop faces configured to accurately place the rope relative to the jig, and thereby relative to features thereof, particularly relative to guide hole(s) and/or guide edges thereof, when the rope is mounted on the jig, particularly placed against the stop faces. The hole is then pre-drilled into the coating while the rope is mounted on the jig.
In a preferred embodiment, said jig comprises one or more guide holes for guiding a drill bit of a drill, and each said pre-drilling is carried out by drilling through a guide hole while the rope is mounted on the jig.
In a preferred embodiment, said plurality of stop faces comprised in the jig are configured to accurately place the rope relative to the jig such that when the rope is mounted on the jig, each guide hole points towards the center of the gap between load bearing members which are next to each other.
In a preferred embodiment, said jig comprises at least a first stop face for supporting the thickness directional side (i.e. flank) of the rope and a second stop face for supporting the width directional side of the rope, and each said guide hole is at a distance from the first stop face corresponding to the distance (as measured in width direction of the rope) between the thickness directional side of the rope and the center of the gap between the load bearing members of the rope which are next to each other (as measured in width direction of the rope). The second face is preferably orthogonal to the first face whereby the jig is well suitable for being used with belt-shaped ropes. Preferably, the jig comprises two of said first stop faces (one for each thickness directional sides, i.e. flanks, of the rope) at a distance from each other corresponding to the width of the rope.
In a preferred embodiment, said rope is belt-shaped, i.e. larger in width direction than thickness direction.
In a preferred embodiment, said plurality of stop faces comprised in the jig are configured to accurately place the rope relative to the jig such that when the rope is mounted on the jig an end of the rope can extend/extends over a guide edge extending in width direction of the rope, and after said mounting the rope is cut, e.g. by sawing, along the guide edge in width direction of the rope.
In a preferred embodiment, said mounting comprises tightening the hoisting rope immovably on the jig, in particular against stop faces of the jig.
In a preferred embodiment, the jig preferably comprises parts, preferably two opposing halves, each comprising stop faces, and said parts defining an inside space wherein the rope can be inserted, said parts being movable towards each other such that the inside space is constricted, at least some of the stop faces of the jig thereby being movable towards the rope placed in the inside space. Said tightening is performed with tightening means such as tightening screws for moving the parts towards each other such that the inside space is constricted, whereby stop faces of the jig compress against the rope from plural directions.
In a preferred embodiment, said method comprises placing beside the end of the hoisting rope one or more plate elements, in particular such that they form a stack, said one or more plate elements including at least the conductive plate element, and said screwing is carried out while the rope and one or more plate elements placed beside the end thereof, including at least the conductive plate element, are mounted on the jig, preferably such that at least the rope is immovable relative to the jig. This is preferably, but not necessarily, performed such that the components are stacked outside the jig. For this purpose after said pre-drilling, the rope is removed from the jig. Then, the method comprises placing beside the end of the hoisting rope one or more plate elements, in particular such that they form a stack, said one or more plate elements including at least the conductive plate element, and thereafter mounting the rope and said one or more plate elements, including at least the conductive plate element, together on the jig, said mounting comprising tightening the stack in the jig, preferably such that at least the rope is immovable in the jig, and after the mounting said screwing is carried out while the rope and said one or more plate elements are mounted on the jig.
In a preferred embodiment, for enabling screwing the screw member(s) into the rope while the rope is mounted on the jig, the jig comprises an opening through which the screw member(s) can be screwed into the rope.
In a preferred embodiment, said conductive plate element has been pre-formed before beginning the method on installation site, such as in a factory, to comprise an opening, preferably a hole, through which a screw member can be placed to extend.
In a preferred embodiment, the stack is mounted on the jig such that the hoisting rope and said one or more plate elements are placed relative to each other such that the opening of the jig, the opening of the conductive plate element and the predrilled hole are all eclipsed such that a screw member can be screwed through the openings into the pre-drilled hole.
It is also brought forward a new electrical contact arrangement on an end of a hoisting rope of a hoisting apparatus, which hoisting rope comprises a non-conductive coating, and a plurality of adjacent conductive load bearing members for bearing the load exerted on the rope in longitudinal direction thereof embedded in the coating and extending parallel to each other and to the longitudinal direction of the hoisting rope unbroken throughout the length of the rope, the coating forming the surface of the hoisting rope and extending between adjacent load bearing members thereby isolating them from each other, which electrical contact arrangement comprises a conductive plate element attached on the end of the hoisting rope; and at least one threaded screw member attaching the conductive plate element immovably beside the end of the hoisting rope, which threaded screw member is screwed into the rope such that it extends centrally between load bearing members next to each other the threads thereof being in contact with both of said load bearing members next to each other, the threaded screw member being made of conductive material, and the conductive plate element is in conductive connection with both of said load bearing members next to each other via said at least one threaded screw member. The threaded screw member thereby connects the contact element conductively with both said load bearing members.
In a preferred embodiment, said conductive plate element is a contact element directly coupled/couplable with a contact element of a source of electricity. Thereby, said conductive plate element can serve as a contact interface via which electricity can be conducted into both of said load bearing members from the source of electricity.
In a preferred embodiment, said conductive plate element comprises a portion protruding away from the rope forming a contact pin that can be directly coupled with another contact element forming a counterpart for the pin, such as with a contact element of a source of electricity.
In a preferred embodiment, said threaded screw member has a screw-head compressed against the conductive plate element directly or indirectly via only conductive members such as one or more washers.
In a preferred embodiment, a non-conductive support plate element is provided between the rope and the conductive plate element. The conductive plate element is then placed beside the end of the hoisting rope such that it leans directly against the support plate which leans directly against the rope, but the conductive plate element could of course alternatively be placed beside the end of the hoisting rope such that it leans directly against the rope.
In a preferred embodiment, said hoisting rope comprises at least four of said load bearing members, and said electrical contact arrangement comprises at least two of said conductive plate elements attached on the end of the hoisting rope, said two conductive plate elements being separate from each other and in conductive connection with mutually different load bearing members next to each other in the defined way. Then one of said conductive plate elements is in conductive connection with first pair of load bearing members next to each other via at least one first screw, and the other of said conductive plate elements is in conductive connection with second pair of load bearing members next to each other via at least one second screw.
In a preferred embodiment, the electrical contact arrangement has been obtained with the method according to any of the preceding claims. Particularly, by using the jig a process steps requiring accuracy can be carried out quickly with excellent quality.
It is also brought forward a new arrangement for condition monitoring of a hoisting rope of a hoisting apparatus wherein load bearing members of the hoisting rope that are next to each other, are in conductive connection with each other and form part of an electrical circuit whereto a source of electricity is connected, which arrangement for condition monitoring comprises a monitoring unit for monitoring one or more electrical parameter of the electrical circuit so as to determine condition of the circuit, the condition monitoring unit being configured to deduce condition of the load bearing members of the rope, based on condition of the circuit, the arrangement comprising on at least one end of the hoisting rope an electrical contact arrangement as defined in any of the preceding claims connecting said load bearing members of the hoisting rope that are next to each other to be in conductive connection with each other.
In a preferred embodiment, said conductive plate element of the electrical contact arrangement is a contact element directly coupled with a contact element of a source of electricity U. Thereby, said conductive plate element serves as a contact interface via which electricity is conducted into both of said load bearing members from the source of electricity. The contact element of the source of electricity can be one serving as a positive or negative terminal thereof.
In a preferred embodiment, said conductive plate element comprises a portion protruding away from the rope forming a contact element in the form of a contact pin that is directly coupled with another contact element such as with a contact element of a source of electricity. The contact element of the source of electricity can be one serving as a positive or negative terminal thereof.
In a preferred embodiment, said hoisting rope comprises at least four of said load bearing members, and said electrical contact arrangement comprises at least two of said conductive plate elements attached on the end of the hoisting rope, said two conductive plate elements being separate from each other and in conductive connection with mutually different load bearing members next to each other in the defined way.
In a preferred embodiment, said load bearing members are made of composite material comprising electrically conducting reinforcing fibers in polymer matrix, said reinforcing fibers preferably being carbon fibers.
Preferably over 50% proportion of the surface area of the cross-section of the load bearing member consists of the aforementioned electrically conducting reinforcing fibers. Thereby, good conductivity can be ensured. The reinforcing gibers will be in contact with each other randomly along their length whereby electricity brought into the load bearing member by the screws will be conducted within substantially the whole cross section of the load bearing member. Preferably, substantially all the remaining surface area is of polymer matrix. To be more precise preferably 50%-80% of the surface area of the cross-section of the load bearing member is of the aforementioned reinforcing fiber, most preferably such that 55%-70% is of the aforementioned reinforcing fiber, and substantially all the remaining surface area is of polymer matrix. In this way conductivity and longitudinal stiffness of the load bearing member are facilitated, yet there is enough matrix material to bind the fibers F effectively to each other. The best results are achieved when approx. 60% of the surface area is of reinforcing fiber and approx. 40% is of matrix material.
In a preferred embodiment, each said load bearing member is parallel with the length direction of the rope. Furthermore, it is preferable that said reinforcing fibers are parallel with the length direction of the rope. Thereby the fibers are also parallel with the longitudinal direction of the rope as each load bearing member is oriented parallel with the longitudinal direction of the rope. This facilitates further the longitudinal stiffness of the rope among other properties highly appreciated in a hoisting rope.
In a preferred embodiment, the reinforcing fibers of each load bearing member are distributed in the polymer matrix of the load bearing member in question and bound together by it to form a one integral piece. The reinforcing fibers of each load bearing member are then preferably substantially evenly distributed in the polymer matrix of the load bearing member in question.
In a preferred embodiment, the module of elasticity E of the polymer matrix is over 2 GPa, most preferably over 2.5 GPa, yet more preferably in the range 2.5-10 GPa, most preferably of all in the range 2.5-3.5 GPa. In this way a structure is achieved wherein the matrix essentially supports the reinforcing fibers, in particular from buckling. One advantage, among others, is a longer service life. With this kind of material of the load bearing members, the tendency to straighten is particularly strong, whereby in this context the measures for alleviating the problems of straightening of rope during installation are particularly advantageous.
The elevator is preferably such that the car thereof is arranged to serve two or more landings. The hoisting rope is preferably arranged to suspend at least the elevator car. The elevator preferably controls movement of the car in response to calls from landing and/or destination commands from inside the car so as to serve persons on the landing(s) and/or inside the elevator car. Preferably, the car has an interior space suitable for receiving a passenger or passengers, and the car can be provided with a door for forming a closed interior space.
In the following, the present invention will be described in more detail by way of example and with reference to the attached drawings, in which
The foregoing aspects, features and advantages of the invention will be apparent from the drawings and the detailed description related thereto.
The arrangement for condition monitoring comprises an electrical contact arrangement C1, C2 provided on each end of the hoisting rope 1, whereby individual load bearing members 3 are connected to other electrically conducting members of the circuit. Thereby, each load bearing member 3 is arranged to form part of said electrical circuit in the arrangement for condition monitoring of said hoisting rope 1.
In the illustrated embodiment, the rope 1 comprises four load bearing members 3. On the first end (on the right in
On the first end of the hoisting rope 1 the load bearing members 3 next to each other have been conductively connected with an electrical contact arrangement C1. This electrical contact arrangement C1 comprises a first and second conductive plate element 4a,4b attached on the end of the hoisting rope 1 separate from each other, which conductive plate element 4a,4b are in conductive connection with different pairs of load bearing members 3. The electrical contact arrangement C1 comprises at least one threaded screw member 5, in this case two of them, attaching each conductive plate element 4a,4b immovably beside the end of the hoisting rope 1, which threaded screw member 5 is screwed into the hoisting rope 1, in particular into the coating 2 thereof, such that it extends centrally between a pair of load bearing members 3 next to each other the threads thereof being in contact with both of said pair of load bearing members 3 next to each other. The threaded screw member 5 is made of conductive material, and each conductive plate element 4a,4b is in conductive connection with both of said load bearing members 3 next to each other via said threaded screw members 5. The threaded screw member 5 thereby connects the conductive plate element 4a,4b conductively with both of said load bearing members 3 next to each other. The threaded screw members 5 are preferably threaded screws.
Each of said conductive plate elements 4a, 4b is a contact element coupleable directly with another contact element that does not form part of the rope or the electrical contact arrangement C1, said another element in this case being a contact element 6a,6b of a source of electricity U. Thus, each conductive plate element 4a, 4b can serve as a contact interface via which an electrical connection can be established between the load bearing members 3 next to each other and the source of electricity U. As illustrated in
On the second end of the hoisting rope 1 there is an electrical contact arrangement C2. This electrical contact arrangement C2 comprises a conductive plate element 4 attached on the end of the hoisting rope 1, which conductive plate element 4 is in conductive connection with all of said load bearing members 3. The electrical contact arrangement C2 comprises several threaded screw members 5, attaching the conductive plate element 4 immovably beside the end of the hoisting rope 1. Threaded screw members 5 have been screwed into the hoisting rope 1, in particular into the coating 2 thereof, such that one extends centrally between each pair of load bearing members 3 next to each other the threads thereof being in contact with both of the load bearing members 3 next to each other. The threaded screw member 5 is made of conductive material, and the conductive plate element 4 is in conductive connection with all of said load bearing members 3 next to each other via said threaded screw members 5. Each threaded screw member 5 thereby connects the contact element 4 conductively with both of the load bearing members 3 next to each other between which it has been screwed.
As shown in the
With each arrangement C1,C2 the threaded screw member 5 is electrically connected with the conductive plate element 4;4a,4b. As shown in the
The conductive plate element 4;4a,4b is preferably made of metal. The non-conductive coating 2 is preferably made of polymer material, most preferably of elastomer, such as polyurethane. Said conductive load bearing members 3 are preferably made of composite material comprising reinforcing fibers embedded in polymer matrix, which reinforcing fibers are conductive. Most preferably said fibers are carbon fibers, whereby the rope is well suitable for elevator use particularly owing to its superb properties in terms of load bearing capacity and weight.
As shown in the
Each electrical contact arrangement C1,C2 can be manufactured with the method as described elsewhere in the application. A preferred embodiment of the method will be described in details in the following referring to
In the preferred embodiment of the method, as illustrated in
The method comprises first providing a rope 1 as well as the jig 10, such as the one illustrated in
After the rope has been preprocessed while it is mounted on the jig 10, i.e. after said pre-drilling and/or said cutting performed on the rope 1 while it is mounted immovably on the jig 10, the rope 1 is removed from the jig 10. After this, the method comprises placing beside the end of the hoisting rope 1 one or more plate elements 4; 4a,4b; 7 such that the rope 1 and the plate elements form together a stack, said one or more plate elements including at least the conductive plate element 4;4a,4b, and thereafter mounting the rope 1 and said one or more plate elements together in the jig 10 as a stack. The aforementioned plate elements, including at least the conductive plate element 4;4a,4b are after this attached immovably beside the hoisting rope 1 while the hoisting rope 1 and the aforementioned plate elements 4;4a,4b are mounted on the jig 10. As illustrated in
The jig 10 is more specifically such that it comprises at least a first stop face F1a for supporting the thickness directional side (i.e. flank) of the rope 1 and a second stop face F2a for supporting the width directional side of the rope 1. Each said guide hole 11 is at a distance from the first stop face F1a corresponding to the distance (as measured in width direction of the rope) between the thickness directional side (i.e. the flank) of the rope 1 and the center of the gap between the load bearing members 3 of the rope 1 which are next to each other (as measured in width direction of the rope). The second stop face F2a is orthogonal to the first stop face F1a. Moreover, the jig 10 comprises two of said first stop faces F1a and F1b (one for each thickness directional side of the rope 1, i.e. flanks) at a distance from each other corresponding to the width of the rope 1.
As mentioned, the hoisting rope 1 is belt-shaped, and thereby substantially larger in width direction w than in thickness direction t. Thereby the total resistance of the rope against bending around an axis extending in width direction w of the hoisting rope 1 is reduced. The width/thickness-ratio of the rope 1 is preferably at least 2 whereby the advantages related to the bending resistance become clearly substantial. Thus, also several load bearing members 3 can be fitted in the rope 1 adjacently.
The fibers F used in the preferred embodiments are substantially untwisted in relation to each other, which provides them said orientation parallel with the longitudinal direction of the rope 1. This is in contrast to the conventionally twisted elevator ropes, where the wires or fibers are strongly twisted and have normally a twisting angle from 15 up to 30 degrees, the fiber/wire bundles of these conventionally twisted elevator ropes thereby having the potential for transforming towards a straighter configuration under tension, which provides these ropes a high elongation under tension as well as leads to an unintegral structure.
The reinforcing fibers F are preferably long continuous fibers in the longitudinal direction of the load bearing member, the fibers F preferably continuing for the whole length of the load bearing member 3 as well as the rope R. Thus, the load bearing ability, good conductivity as well as manufacturing of the load bearing member 3 are facilitated. The fibers F being oriented parallel with longitudinal direction of the rope 1, as far as possible, the cross section of the load bearing member 3 can be made to continue substantially the same in terms of its cross-section for the whole length of the rope 1. Thus, no substantial relative movement can occur inside the load bearing member 3 when it is bent.
As mentioned, the reinforcing fibers F are preferably distributed in the aforementioned load bearing member 3 substantially evenly, in particular as evenly as possible, so that the load bearing member 3 would be as homogeneous as possible in the transverse direction thereof. An advantage of the structure presented is that the matrix m surrounding the reinforcing fibers F keeps the interpositioning of the reinforcing fibers F substantially unchanged. It equalizes with its slight elasticity the distribution of a force exerted on the fibers, reduces fiber-fiber contacts and internal wear of the rope, thus improving the service life of the rope 1. The composite matrix m, into which the individual fibers F are distributed as evenly as possible, is most preferably made of epoxy, which has good adhesiveness to the reinforcement fibers F and which is known to behave advantageously with carbon fiber. Alternatively, e.g. polyester or vinyl ester can be used, but alternatively any other suitable alternative materials can be used.
As above mentioned, the matrix m of the load bearing member 3 is most preferably hard in its material properties. A hard matrix m helps to support the reinforcing fibers F, especially when the rope bends, preventing buckling of the reinforcing fibers F of the bent rope, because the hard material supports the fibers F efficiently. To reduce the buckling and to facilitate a small bending radius of the load bearing member 3, among other things, it is therefore preferred that the polymer matrix m is hard, and in particular non-elastomeric. The most preferred materials for the matrix are epoxy resin, polyester, phenolic plastic or vinyl ester. The polymer matrix m is preferably so hard that its module of elasticity E is over 2 GPa, most preferably over 2.5 GPa. In this case the module of elasticity E is preferably in the range 2.5-10 GPa, most preferably in the range 2.5-3.5 GPa. There are commercially available various material alternatives for the matrix m which can provide these material properties.
Preferably over 50% of the surface area of the cross-section of the load bearing member 3 is of the aforementioned electrically conducting reinforcing fiber. Thereby, good conductivity can be ensured. Fibers F will be in contact with each other randomly along their length whereby electricity brought into the load bearing member by the screws 5 will be conducted within substantially the whole cross section of the load bearing member. To be more precise preferably 50%-80% of the surface area of the cross-section of the load bearing member 3 is of the aforementioned reinforcing fiber, most preferably such that 55%-70% is of the aforementioned reinforcing fiber, and substantially all the remaining surface area is of polymer matrix. In this way conductivity and longitudinal stiffness of the load bearing member 3 are facilitated yet there is enough matrix material to bind the fibers F effectively to each other. Most preferably, this is carried out such that approx. 60% of the surface area is of reinforcing fiber and approx. 40% is of matrix material.
In the embodiments illustrated in
In the illustrated embodiment, the rope 1 comprises four load bearing members 3. Of course, alternative configurations are possible, where the contact arrangement C1,C2 is implemented with a rope provided with some other number of load bearing members 3.
The conductive plate element 4;4a;4b is most preferably made of a metal plate. It preferably comprises at least a completely flat portion for being set parallel with the width directional side of the rope 1. It may be completely flat as illustrated in the preferred embodiments, or alternatively comprise bends, e.g. made by bending a plate billet. It may additionally comprise perforations, e.g. made by perforating a plate billet.
Use of a jig is of particular value, when said load bearing members are made of composite material comprising electrically conducting reinforcing fibers in polymer matrix. With this type of load bearing members, establishing the electrical connection would be otherwise difficult owing to the mechanical properties of the composite material of the load bearing members. In particular, accuracy of the position of the screw is important because the material does not by itself guide the screw very effectively in a central position. Nor does the material, particularly when fragile, endure well forces caused by a misdirected screw. By using the jig 10, accuracy of the position of the screw can be ensured such that a proper and reliable electrical contact results with both of the load bearing next to each other.
When referring to conductivity, in this application it is meant electrical conductivity.
It is to be understood that the above description and the accompanying Figures are only intended to teach the best way known to the inventors to make and use the invention. It will be apparent to a person skilled in the art that the inventive concept can be implemented in various ways. The above-described embodiments of the invention may thus be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that the invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims and their equivalents.
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