Patent Application
20110088926
The invention relates to an electrical line for the connection of non-stationary electrical loads to a power source, which line has a line core surrounded by a jacket of insulating material, in which line core wires consisting of insulated electrical conductors used both for the transmission of data and for supplying power are arranged and in which the line core is surrounded by an electrical screen having two layers, one of which is constructed as braid or stranded cover layer of copper wires and the other one of which is constructed of a fleece material consisting of synthetic material made electrically conductive.
Such a line is disclosed in EP-A-1 589 541.
Such lines are used, for example, in drag chains and for connecting non-stationary devices, particularly robots, to a voltage or signal source. The lines must be capable of carrying mechanical loads, with a flexural strength which remains uniform for a long time. They should also remain easily bendable within a wide range of temperatures which is, for example, between −40° C. and +80° C. Apart from resistance against temperature and torsion, their electrical properties are of special significance for such lines. This refers especially to the conductors provided for the transmission of data, with operating frequencies of over 100 MHz.
Apart from other transmission elements, the known line according to DE 101 62 739 A1 has two data transmission lines and one power line used for supplying power which are in each case surrounded by an electrical screen. The data transmission lines in each case consist of a pair of wires with two insulated electrical conductors and the power line has four wires of insulated electrical conductors. This known line has been successful in practice. However, its production is complex.
In EP-A-1 589 541 mentioned initially, an electrical line for the connection of non-stationary electrical loads to a power source is described which has a line core surrounded by a jacket of insulating material, in which line core wires consisting of insulated electrical conductors are arranged which are used both for the transmission of data and for supplying power. The line core of this known line is surrounded by an electrical screen having two layers, one of which is constructed as braid or stranded cover layer of copper wires whilst the other one has at least one layer of a fleece material consisting of synthetic material and made electrically conductive. For the data transmission, a pair of wires which is surrounded by shielding is placed in the line core. In the mutually opposite interstices between the wires of the pair of wires, a supply wire each used for supplying power is arranged outside the shielding.
The invention is based on the object of specifying a line of the type described initially which can be produced in a more compact and simple manner and is suitable for transmitting data with operating frequencies of over 100 MHz.
According to the invention, this object is achieved
This line can be produced in a simple manner in conventional technology. In the line core, it consists of four wires, stranded together to form one star quad, for the data transmission and of at least two wires for supplying power which are stranded together in a preferred embodiment. The star quad is a symmetric structure of two pairs of wires all of which have the same length. Differences in delay for the data on the two pairs can be eliminated and crosstalk between the two transmission circuits is minimized by the good electrical decoupling of the two pairs given by the symmetry of the star quad. The dimensions of the star quad are also kept small because it does not have its own external electrical screen, also called element screen. This also applies to the wires used for supplying power. Because of the lacking element screens, the star quad and the wires used for supplying power can also be simply stranded together. The layer of insulating material, preferably a fleece material of polypropylene, provides a sufficiently low capacity between the screen and the line core. The braid or the stranded cover layer of copper wires as one layer of the screen produces an optimized line attenuation. As further layer of the screen, the metallized fleece material, which forms a layer of electrically conductive material closed all around, provides the electrical shielding against high-frequency electromagnetic fields over a wide range of frequencies. The metal existing in the fleece material, which is preferably copper, is deposited from the vapour phase. It is deposited not only on the outer surface of the fleece material but also penetrates it and encloses its inner fibres which are held together unsorted in the fleece material as is known. Accordingly, the fleece material is coated in a “penetrating” manner. As a result, it has a metal layer which, although it is porous, is still almost complete and results in a covering of the enclosed line core with electrically effective metallic material of >85%. To form a corrosion or oxidation protection layer, nickel or silver, for example, can be deposited in addition to the copper.
Exemplary embodiments of the subject matter of the invention are represented in the drawings, in which:
In the drawings, a preferred embodiment of the line is shown in which two wires used for supplying power are stranded together to form one pair of wires. The line should have at least two wires used for supplying power which are stranded together with a star quad which is also present in the line core. In the description following, the line is described for the preferred embodiment—also representative of the other possible embodiments.
The line according to
Over the line core, a layer 5 of insulating material is placed which is surrounded by an electrical screen. The screen has a first layer 6 resting against the layer 5, which layer 6 is preferably constructed as braid or stranded cover layer of copper wires. Over the first layer 6 of the screen, a second layer 7 of the latter is arranged which consists of fleece material made electrically conductive. An outer jacket 8 of insulating material surrounds the second layer 7 of the screen.
The conductors of the wires 2 of the star quad S are preferably constructed as stranded conductors consisting of seven copper wires, with a cross section of, for example, 0.25 mm2. To enlarge the electrically conductive cross section of these conductors, six thinner copper wires can be arranged additionally in the outer interstices of the wires. This may lead to a further reduction in the line attenuation. The wires of the stranded conductor can also consist of a copper alloy such as, for example, a copper/tin alloy. To maintain a predetermined diameter of, for example, 1.05 mm at a maximum for the wires 2, the insulation of the conductors consists of solid material to be extruded dimensionally accurately, especially of polyethylene (PE), polypropylene (PP) or of a fluoropolymer (FEP, PTFE, PFA) if the line is to be used in regions with high temperatures.
The star quad S is produced in conventional technology by stranding four wires 2, preferably by reversing the wires so that a twist-free star quad with dimensionally accurately positioned wires is produced.
The conductors of the wires 1 of the pair of wires A provided for supplying power have, for example, a cross section of 0.38 mm2. The diameter of the wires 1 can also be, for example, 1.05 mm at a maximum.
The layer 5 of insulating material advantageously consists of a PP fleece material, of a foamed PP or also of a low-density PTFE if the line is to be used at high temperatures. A ribbon of such a material can be preferably wound with overlap around the line core. In a modified embodiment, the layer 5 can also be constructed as a so-called inner sheath which also fills up the interstices between the star quad S and the pair of wires A. The separate filling elements 3 and 4 are then omitted.
The copper wires of the braid or of the stranded cover layer, respectively, can be tin-plated. When the line is used at higher temperatures, silver- or nickel-plated copper wires can also be used.
In a preferred embodiment, the fleece material of the second layer 7 of the screen is a polyester. Especially at higher operating temperatures, it can also consist of other suitable synthetic materials such as, for example, aramide or glass fibres. Its wall thickness is preferably between 80 μm and 300 μm. For its metallization, at least one electrically highly conductive metal is used, especially copper or silver. A copper layer produced in this way can be provided with an additional nickel layer. The respective metal is deposited on the fleece material from the vapour phase by means of plasma technology.
In this process, the metal vapours also penetrate into the relatively open fibre structure of the fleece material and enclose the fibres held together unsorted, which are located there. Overall, a metal layer which, although it is porous, is almost closed is generated on and in the fleece material which results in a covering of >85% for an enclosed object—in this case it is the first layer 6 of the screen. The fleece material is preferably wound as a ribbon with overlap around the first layer 6 of the screen.
The jacket 8 consists, for example, of polyvinyl chloride, polyurethane, a thermoplastic elastomer, of silicone or of a fluoroelastomer.
The line according to
In the embodiment of the line according to
