Slip ring transducer
09742135 · 2017-08-22
Assignee
Inventors
Cpc classification
Y10T29/49011
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
H01R39/00
ELECTRICITY
F03D9/25
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
Y02E10/72
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
International classification
H01R39/00
ELECTRICITY
F03D80/80
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F03D9/25
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
Abstract
The invention relates to a slip ring assembly of a slip ring transducer for transducing electrical signals between a stationary part and a part which rotates around an axis of rotation, comprising: at least one slip ring for transducing one of the electrical signals between the slip ring and at least one slip element trailing thereon, in particular a brush, and a slip ring shaft for securing the at least one slip ring thereon, the slip ring shaft having guiding channels distributed along its circumference in order to receive electrical lines for electrically connecting the at least one slip ring.
Claims
1. A slip ring assembly of a slip ring transducer for transmitting electrical signals between a static part and a rotating part, the slip ring assembly comprising: at least one slip ring coupled to the rotating part for transmitting one of the electrical signals between the at least one slip ring and at least one rubbing element coupled to the static part; a slip ring shaft fixed to the at least one slip ring, wherein the slip ring shaft comprises guide channels around its circumference configured to receive electrical cables and electrically couple the cables to the at least one slip ring; and at least one insulating body around the slip ring shaft, wherein the slip ring shaft has a profile and the insulating body has a counter profile so that the insulating body, along with the counter profile, is configured to be moved in an axial direction along a profile of the slip ring shaft, wherein the profile and the counter profile mesh in such a way to provide a torque-proof connection.
2. The slip ring assembly according to claim 1, wherein the at least one rubbing element is a brush.
3. The slip ring assembly according to claim 1, wherein the slip ring shaft has an inner circumference and radial supports that extend outwardly from the inner circumference, the radial supports including the guide channels.
4. The slip ring assembly according to claim 1, wherein the at least one slip ring is made from a bronze slide bearing semi-finished product.
5. The slip ring assembly according to claim 1, further comprising a threaded weld stud configured to attach an electrical connector cable from at least one slip ring, a soldered connector on the slip ring.
6. The slip ring assembly according to claim 1, comprising a plurality of slip ring sections in an axial direction, and that each slip ring section forms a galvanically connected unit, and that the slip ring sections of different axial dimensions have different slip rings of a same size, so that each axial dimension of each slip ring section is achieved by the number of slip rings used.
7. The slip ring assembly according to claim 1, wherein the slip ring shaft has a through-hole having a longitudinal axis that is co-axial with a rotational axis of the slip ring assembly.
8. The slip ring assembly according to claim 7, wherein the at least one insulating body is configured to electrically insulate at least one of: two adjacent slip ring assemblies from one another; a slip ring from the slip ring shaft; and at least one of the electrical cables in the guide channels.
9. The slip ring assembly according to claim 1, wherein the at least one insulating body is a plurality of insulating bodies and the at least one slip ring is a plurality of slip rings.
10. The slip ring assembly according to claim 9, wherein the plurality of insulating bodies, each having identical cross-sections and differing lengths or differing axial dimensions as each other, wherein the plurality of insulating bodies are configured to mesh together on the slip ring shaft.
11. The slip ring assembly according to claim 9, wherein the plurality of insulating bodies have stepped edges to fit with corresponding stepped edges of an adjacent insulating body of an adjacent slip ring assembly.
12. The slip ring assembly according to claim 9, wherein at least one of the plurality of insulating bodies is used as a marginal insulating body to electrically insulate the at least one slip ring in a radial direction and in an axial direction, and at least one of the insulating bodies is used as a spacer insulating body to electrically insulate at least one slip ring in a radial direction only, such that the spacer insulating body is specifically configured in an axial direction between two marginal insulating bodies.
13. The slip ring assembly according to claim 9, wherein some of the plurality of insulating bodies on the slip ring shaft are juxtaposed, and in combination form at least one axial cable duct configured to receive one of the at least one electrical cables, wherein the at least one cable duct is insulated by the insulating bodies from other slip rings and from the slip ring shaft.
14. The slip ring assembly according to claim 9, wherein at least one of the plurality of insulating bodies includes an external cylinder section and at least one ridge is located on the external cylinder section and is configured to assist in coupling the cylinder section to the slip rings.
15. The slip ring assembly according to claim 9, wherein the plurality of slip rings and the plurality of insulating bodies are replaceable, wherein the plurality of slip rings and the plurality of insulating bodies are configured to slide onto the slip ring shaft.
16. A slip ring transducer to transmit electrical signals between a static part and a rotating part that rotates around a rotation axis, the slip ring transducer comprising: a slip ring assembly including: at least one slip ring coupled to the rotating part for transmitting one of the electrical signals between the slip ring and at least one rubbing element coupled to the static part; a slip ring shaft fixed to the at least one slip ring, wherein the slip ring shaft comprises guide channels around its circumference configured to receive electrical cables and electrically couple the cables to the at least one slip ring; and an insulating body around the slip ring shaft, wherein the slip ring shaft has a profile and the insulating body has a counter profile so that the insulating body, along with the counter profile, is configured to be moved in an axial direction along the profile of the slip ring shaft, and the profile and the counter profile mesh in such a way to provide a torque-proof connection.
17. The slip ring transducer according to claim 16, further comprising a signal unit section and a power unit section, the signal unit section and the power unit section each have a fixed mounted section that is rotatable, and both of fixed mounted sections are removably connected by a respective coupling element such that a rotating movement in one of the rotatable mounted sections can be transmitted to the other rotatable mounted section via the coupling element.
18. The slip ring transducer according to claim 17 wherein the coupling element on the power unit is designed as a tappet bushing to hold a corresponding, partially available drive pin on the signal unit.
19. The slip ring transducer according to claim 17, wherein the power unit has a housing configured to be closed by quick release fasteners and at least one of the rotatable mounted sections is mounted using at least one pre-stressed bearing.
20. A wind turbine comprising: a nacelle; an aerodynamic rotor mounted to the nacelle such that the aerodynamic rotor is configured to rotate relative to the nacelle; and a slip ring transducer configured to provide electrical coupling between the nacelle and the aerodynamic rotor, the slip ring transducer including: a slip ring assembly including: a plurality of slip rings coupled to the aerodynamic rotor, each configured to transmit electrical signals between the respective slip ring and at least one brush coupled to the nacelle; and slip ring shafts located in the slip rings, respectively, wherein the slip ring shafts have an inner circumference and supports that extend radially from the inner circumference thereby forming guide channels configured to hold electrical cables for electrically coupling to respective slip ring; and an insulating body around the slip ring shaft, wherein the slip ring shaft has a profile and the insulating body has a counter profile so that the insulating body, along with the counter profile, is configured to be moved in an axial direction along the profile of the slip ring shaft, and the profile and the counter profile mesh in such a way to provide a torque-proof connection.
Description
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
(1) The invention is now described in more detail below using embodiments as examples with reference to the accompanying figures.
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DETAILED DESCRIPTION
(22) Below, similar but not identical elements with identical reference numbers are shown, to underline their functional similarity. Identical embodiments or elements of identical embodiments may be illustrated on different scales.
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(26) The rotating connector 6 can be attached via a driver attachment 14 to a rotating component, e.g., part of an aerodynamic rotor in a wind turbine, such that the rotating connector 6 rotates with this rotor cited as an example, whereby the slip ring shaft 8 rotates with it simultaneously. All connections in this rotating element, which in this example is given as a wind turbine aerodynamic rotor, may be connected to various connector elements 16, which can be arranged entirely differently on the rotating connector 6. This concerns both power connections and signal connections. For clarity, it should be noted that the slip ring transducer 1 can in principle be used to transmit electrical signals, both high-powered electrical signals, specifically supply currents for corresponding electrical devices, and also contains electrical signals which essentially transmit information like control signals or test signals. However, where the power unit 2 and the signal unit 4 and their components differ in the slip ring transducer 1 is in the signal unit 4, the part of the slip ring transducer 1 that basically transmits low power signals, i.e., particularly control and test signals. In contrast to this, the power unit is the part of the slip ring transducer which transmits high power density or high power, i.e., power which is significantly higher than that from the signal unit. Preferably, a ground connection being made via the slip ring transducer—in electro-technical terms—will also be made via the power unit.
(27) Details of the connection between the electrical cables and the rotating connector are irrelevant. In any case, electrical cables lead from the rotating connector 6 to the slip ring shaft 8. Electrical cables intended to transmit low-power signals and which should lead to the signal unit are guided in an axial through-hole, called a central tube 18, to the signal unit connection area 20.
(28) Electrical cables for transmitting high power, which for the sake of simplicity can be referred to as energy cables 22 or power cables 22, are guided into the slip ring shaft 8 outside the central tube 18 in guide channels 24. The power cables 22 are thus attached to a slip ring 28 via a threaded weld stud 26. The threaded weld stud 26 is welded to the slip ring 28 for this reason, and the power cable 22 is firmly screwed onto the threaded weld stud using a cable shoe, which cannot be seen in
(29) The static power unit 12 has brushes 30, which may have different axial lengths, and which rub the slip ring 28 in order to transmit an electric current from the slip ring shaft 8 to the static power unit 12. The electrical energy transmitted between the slip rings 28 and brushes 30 can then be further transmitted from the static power unit via appropriate static connector elements 32 and passed on. The specific embodiment of static connector elements 32 is irrelevant. Incidentally, the transmission direction of the electrical cables, i.e., via electrical current from the rotating parts to the static part, is only cited as an example. Likewise, transmission in the opposite direction is considered as is usual, for example, during the transmission of electrical energy from a wind turbine nacelle to a wind turbine aerodynamic rotor via this type of slip ring transducer 1.
(30) The signal unit 4 shown in
(31) The signal unit 4 is intended to transmit electrical signals with low power, specifically control signals and test signals. These electrical signals are transmitted inwards and outwards via cables inside the central tube 18 of the power unit 2, and via the signal connector 48 and signal mating connector 50 to the rotating part 40 of the signal unit 4. Accordingly, signal connector 48 and signal mating connector 50 are connected to a plug connection while connecting the signal unit to the power unit 2. Accordingly, the signal cables being fed into the power unit 2 inside the central tube 18 are galvanically connected to the signal connector 48. Accordingly, signal cables inside the rotating part 40 of the signal unit 4 are electrically connected or attached to the signal mating connector 50.
(32) Cables from the signal connector 48 are electrically connected with slip rings 52 to further transmit lower power electric signals inside the signal unit 4. Brushes 54 then rub on slip rings 52 in the signal unit 4, as shown in different ways in
(33) To firmly connect the signal unit 4 to the power unit 2, i.e., in the area of signal connector area 20 and the corresponding signal connector area 34, the signal unit 4 has a corresponding connector flange 56. A sealing ring 58 is also used in the area of the connector flange 56 to seal the power unit 2 in a sealing area 60. It should be noted that the scales of the power unit 2 in
(34) Finally, a data cable 62 with a data connector plug 64 on the static part 44 of the signal unit 4 is used to transmit or conduct the low powered signals being transmitted in the signal unit 4.
(35) The section of a partially completed power unit 2 in
(36) A radially constructed bracket 76 for brush seating 78 is used to remove or transmit electrical energy between the slip rings and the static power unit 12 of the power unit. The brush seating 78 is attached to the radial bracket 76 using a fixture 80. Carbon brushes can be inserted into the brush seating 78 to rub the respective slip ring 28 and thereby create an electrical connection between the static power unit 12 and the rotating slip ring assembly 72. In
(37) Otherwise,
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(40) To illustrate the required elements in a slip ring assembly 72, a slip ring 28 is also moved and sits on the insulator jacket section 88 of a marginal insulating body 84. The slip ring 28 therefore covers a jacket opening 92 in the insulator jacket section 88 of the marginal insulating body 84.
(41) Illustrative
(42) Again, please note that
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(44) The marginal insulating body 84 also has six cable duct sections 94. The cable duct sections 94 are used to insert or to axially slide along a slip ring shaft 8 in corresponding guide channels 96, as for example is partially shown in
(45) The cable duct sections 94 of several insulating bodies therefore each connect to an insulator duct, through which at least one electrical cable can be fed. Depending on which insulator duct it is fed through, such an electrical cable can be electrically connected at the corresponding jacket opening 92 to the slip ring 28.
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(47) A cable shoe 206 is used to electrically connect with an electrical cable. This cable shoe takes a corresponding cable and can be firmly and galvanically electrically connected with good conductivity to a loop on the threaded weld stud 26. To illustrate this,
(48) A threaded weld stud 26 is shown in
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(50) Inside the fixing ring 220, there is therefore a shaft section 224, which is firmly connected to the slip ring shaft 8 and is therefore mounted in such a way that it can rotate relative to the fixing ring 220. Contrary to
(51) If a signal unit 4, as shown in
(52) As can also be seen in the overall view in
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(54) Individual sections of the slip ring shaft 8 can be illustrated in the axial top view in
(55) Each arm 240 also has axial thread holes 252, which can be used to attach other elements on both of their front sides via the slip ring shaft 8. This specifically allows a fixed and torsionally rigid connection to be made with or to the rotating connector 6. And this allows a fixed and torsionally rigid connection to be made to the shaft section 224 shown in
(56) The marginal insulating body 84 is shown in two different views in
(57) The cable duct sections 94 are used to carry electrical cables and to enable the most precise placing and sliding onto a slip ring shaft possible.
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(59) Another side of the marginal insulating body 84 shown in
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(62) Using the jacket opening 92 of the marginal insulating body 84 is sufficient to electrically connect a cable. The spacer insulating body 86 therefore has no opening in its jacket 90. Furthermore, the marginal insulating body 84 is also highly stable due to its insulator disc section 74, which supports the provision of jacket openings 92, whereby it counteracts a slight loss of stability due to these jacket openings 92.
(63) Although the spacer insulating body 86 is described as different from the marginal insulating body 84, it still has some of the same elements or sections, specifically the circumferential step 202 and the corresponding circumferential step 262, as well as the cable duct sections 94.
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(65) The slip ring 28 in
(66) Depending on the size of the current being transmitted, and therefore the power being transmitted, the slip ring 28 may have different axial dimensions, i.e., may be different in height pursuant to
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(69) Two of these signal unit braces 41, i.e., those illustrated in
(70) The braces of the signal unit 4 are made of extruded aluminum. This is proposed as a basic principle, not just for the embodiment shown in
(71) The shape is therefore a semicircular square, so that only two edges of the square are present. This shape is expensive to produce because the semicircle requires a relatively major processing, and it would have a poor surface if processing were carried out using corresponding cutting or filing. The two edges mean it cannot be made as a turned part. The arches and the flat surfaces and edges are, however, required for the reasons stated above. Normally, no excessive increases in field strength occur, and therefore flashovers mostly occur at sharp edged places. The semicircle or arches of the semicircle point towards the current-conducting slip rings of the rotating part 40 and here there may be a potential between the slip ring and these earthed signal unit braces 41. Using extrusion for manufacturing makes it possible to manufacture this beneficial shape of this signal unit brace, i.e., cross-section shape.
(72) Moreover, manufacturing using extrusion allows flexibility in the length of the signal unit braces 41. To extend the signal unit 4, the length of the signal unit braces can simply be varied, and therefore larger slip ring transducers with more rings in the signal unit can be made.
(73) Moreover, extrusion gives a good surface. In particular, grit does not stick to the surface and the braces are easier to maintain and clean.
(74) Moreover, during the extrusion process, i.e., during aluminum extrusion as we are suggesting here, it is possible to anodize the workpiece in the factory, i.e., to oxidize the surface in an electrobath and therefore create a thicker oxide coating. The aluminum oxide coating has the useful property of being electrically insulating. Thicknesses of up to 100 μm may be possible here. A thickness of approximately 20 μm is preferably proposed. This is beneficial because a thickness of 15 μm should already have a breakdown voltage of 500-600 V and therefore a thickness of 20 μm has good, sufficient installation for this signal unit 4. The raw braces, i.e., the signal unit braces prior to oxidization, can be several meters long and can be oxidized at that length. This means the oxidization process can be carried out with little or insignificant additional expense.
(75) Therefore, an improved, at least altered slip ring transducer is being proposed, with a roughly radial shaft. This is particularly well-suited as an extrusion shape, and is therefore scalable and allows modular construction and therefore reusability. The type of shaft creates guide channels, like the guide channels 96 for example, and can therefore optimize cabling. The specific bundling or unbundling of cables can also improve heat dispersal. Likewise, electromagnetic compatibility is improved, which is why we are proposing to put signal units inside the central tube of the shaft, i.e., separated from the cabling.
(76) The proposed insulating bodies allow modular construction and scalability. In particular, using different numbers of spacer insulating bodies, including none, allows modular construction, and the insulating bodies essentially only need to be fitted to the shaft. Corresponding circumferential steps improve the insulation between insulating bodies, which will also reduce or prevent creepage paths for currents, since the insulating bodies can fully inter-mesh. Small ridges on the insulating bodies, or at least on a few insulating bodies, may allow the slip rings to be accommodated without play, and therefore improve run out, which can also extend the lifespan.
(77) Slip rings are preferably mounted as semi-finished products above sleeve-bearing bronze bushings, whereby some connectors for connecting electrical cables may be able to be pressed on. Fundamentally different connection techniques can be used. Using sleeve-bearing bushings as semi-finished products gives the slip rings greater stability, which is also supported by manufacturing with strain hardening. This can result in greater resistance to wear and good electrical properties being obtained.
(78) To connect electrical cables, specifically for large cross-sections like 35 mm.sup.2, 50 mm.sup.2 and 70 mm.sup.2, different variants are proposed.
(79) One variant is to solder a connector. Here, a connector can be soldered to the slip ring and this piece can be fed into a guide such as a dovetail groove and soldered onto a specified position. A cable is fed into this connector in turn and is fixed, soldered, for example.
(80) Another or an additional variant is to press on a connector. Here, for example, one of the connectors described in the previous variant can be pressed onto an extruded slip ring during manufacturing. This would avoid any soldering.
(81) Yet another variant involves using a sleeve-bearing bushing with flat contact surfaces. A threaded weld stud can be fitted to these flat contact surfaces using arc welding. The respective cabling can now be easily laid on these threaded weld studs using cable shoes.
(82) An interface between the signal unit and the power unit is also proposed, which is equipped with a mechanical drive device. This is configured so that a clamping pin, introduced or provided for in the signal unit, is inserted into a bushing in the power unit. A clamping pin allows a play-free drive. The bushing is designed as a wearing part and can easily be replaced, namely through one of the corresponding holes in the sleeve.
(83) We also propose closing the power unit housing using quick release fasteners or quick action fasteners to allow quick maintenance. This type of quick action fastener may also include a spacer bracket for sealing.
(84) We likewise propose the use of pre-stressed bearings, which offer a defined bearing load and a greater lifespan, and also ensure play-free mounting.
(85) In this case, a predefined voltage is applied to the bearing, in particular a roller bearing, by a disc spring in order to force the corresponding rolling element back into a predefined configuration, namely an “O configuration”. This causes high bearing rigidity, which is characterized by limited tilting and/or high torque resistance. This high bearing rigidity is particularly important for the signal slip ring, i.e., the slip ring of the signal unit, and the sensors installed in it.
(86) A one-sided bearing for the signal unit is also proposed. Here, the housing can be designed to be completely removed, which allows for thorough and simple maintenance. Pre-stressed bearings can also be used here for a defined bearing load, thereby providing greater lifespan and play-free mounting.
(87) Using individual slip rings with set axial dimensions is also proposed, which can be described as length or width, depending on the point of view. These dimensions may be one of three variants, i.e., three set axial dimensions, e.g., 29 mm, 54 mm and 79 mm. These will be arranged according to defined current load capacities, therefore 150 A, 300 A or 450 A in the example given.
(88) Using a bronze slide bearing semi-finished product for the slip ring material is also proposed. Thus another well-known material from other areas can be used. Stability can accordingly be increased here, with acceptable electrical properties.
(89) Two different insulating bodies are also proposed, namely a marginal insulating body and a spacer insulating body as specified above. The marginal insulating body will be used to separate slip rings of different potentials and a spacer insulating body, which can be attached in many ways, to take different widths of slip rings. For this purpose, insulated cable channels will be provided along the shaft, specifically using the cable duct sections 94 described.
(90) For this purpose, a profiled shaft like the one in the insulating body is proposed, which is extruded in particular.
(91) Preferably, cables are connected to the slip ring via threaded weld studs attached by arc welding.
(92) This therefore allows a modular power unit, made up of different numbers of slip rings and insulating bodies.
(93) Likewise, it is proposed to use coupling to separate the signal unit from the power unit.
(94) This specifically creates a modular system, in which a power slip ring transducer and a signal slip ring transducer are separated by electrical and mechanical coupling, and form two individual slip ring transducers. It is also possible to attach multiple internal connectors to the slip ring in order to transfer differently sized currents. For this purpose, the corresponding cables can be supplied to the slip ring by multiple guide channels or cable ducts, and the corresponding insulating body, specifically the marginal insulating body, has multiple openings for this purpose, specifically jacket openings.
(95) Various internal cables, which specifically may have different cross-sections or be different in number, may be fitted using a single connector on each ring.
(96) A slip ring is preferably made of extruded bronze semi-finished product, known as slide bearing bronze, and can be shortened to a suitable ring width, or suitable axial dimension.
(97) An extruded aluminum shaft for the slip ring shaft is preferably proposed, which can be shortened to meet requirements.
(98) We also propose a single carbon brush holder, at least for the power unit, which has a specified width, so that an appropriate slip ring can be used for the required output, i.e., which is suitably adapted to the required output of the carbon brush holder on the corresponding slip ring.
(99) Using carbon brush holders with pockets to hold a longer carbon brush, when using a self-recoiling spring to guarantee the best possible pressing force throughout the entire life of the system, can increase the lifespan. Increasing the lifespan may also be achieved by using pre-stressed bearings, to guarantee the best possible rolling ratio in the bearing. Roller bearings with more grease filling are preferably used to ensure longer lasting lubrication. We also propose using a lubricant with a greater temperature range, so that extreme temperatures do not cause the lubricant to fail.
(100) Avoiding heating the bearing points of the slip ring transducer is also proposed, specifically of the power unit and/or the signal unit at the lowest temperatures. This measure is specifically beneficial when using a wind turbine installed in cold regions or at least in regions where it is cold in winter.
(101) Using a slip ring made of cold-worked, wrought sleeve-bearing bushing material also helps to increase the lifespan because it has higher wear resistance.
(102) Improved heat distribution and therefore avoiding excessively high temperatures is achieved by laying cables inside the extruded aluminum shaft. In this way, there is no dense bundling, because cables from the power unit are fed into individual guide channels in the shaft, specifically the extruded aluminum shaft, and therefore run individually or in combination with a few other cables in such a guide channel. The signal cables run together in a central tube and are therefore separated from the power cables of the power unit. It may still be worth considering bundling the signal cables in the central tube, but this would weaken the separation of power cables. Little heat generation is to be expected in the signal cable either.
(103) The proposed sequence of insulating bodies, and thereby complete meshing, results in greater creepage paths and therefore improved insulation due to the circumferential steps and corresponding circumferential steps.
(104) The proposed variant, i.e., using arc welding to solder a threaded weld stud, means that it is possible to transfer only minimal heat into the slip ring. The input of too much heat and therefore warming, which may locally soften the corresponding cold work area, should be avoided.
(105) Pursuant to one proposal, the insulating body has small ridges, specifically the jacket ridges 260 described, which can deform when the slip ring concerned is moved, so that the slip ring can be held without play.
(106) Quick release fasteners or quick action fasteners allow for better maintenance by offering quick, easy-to-open access to the corresponding area of the slip ring transducer without the need for tools. The signal unit is preferably mounted on one side, in order to allow access to the housing from all the way round, or to enable housing to be removed completely. This allows maintenance-friendly construction.
(107) A drive between the signal unit and power unit, through which the power unit transmits its rotating movement to this signal unit, is preferably designed using a replaceable bushing, specifically a sleeve inserted into a hole. If there is any wear here, the bushing or sleeve are easily replaced.